Were is absolutely correct here. The reason that it's were and not was is that it's a compound subject (which is indicated by and).
Your editor has got a sharp eye. It's definitely awkward, but it's technically correct, which is why you should, as you've suggested, simply re-write the sentence so that the singular item is not the first item in the list (this obviously won't work though if you have all singular items in your list, which I'll explain in a bit).
English grammar does not dictate--to this native speaker's recollection--that the first item in a list indicates the grammatical number. I will say, however, that there were an orange, grapes, two apples ... sounds awful to my ear (and I suspect that this is true with most speakers).
I also think that most speakers make this error without realizing it with expletive constructions (i.e. sentences that are constructed in the order of there/it + be + subject, rather than the more common, active voice, Subject-Verb-Object order). It's generally best to avoid expletive constructions whenever possible (it's not always possible to do so, but in your example, there is unnecessary)
The indefinite article an is ordinarily a marker of singularity, which makes it sound as if it should be was, but with compound subject, that's not the case. It still would be were even if it were**: There were an orange, grapes, an apple, and a cherry [ALL] piled on the plate. Or, even better: An orange, grapes, two apples, and a small pile of cherries were all on the plate.
If the sentence were**, There was an orange, and nothing more, than was would be correct. But because you're talking about multiple subjects that are/were grouped together, the subject is plural.
There are four objects in this list--that's counting the grapes and cherries each as a single unit; technically, there are more--so there's no question that it's plural. This isn't a one-or-the-other situation; it's collective.
A general rule of thumb would be that when you're using and as a conjunction, it's a compound/plural subject, and thus indicating a plural form of the verb. If instead you're using or, then it's singular, regardless of the article.
**I'm using were in two of the above sentences with a singular subjects because I'm using the subjunctive mood; otherwise it'd be was. That's the only time it's ever correct to use were with a singular subject.
From Garner's Modern American English Usage, 3rd Ed.:
Language-Change Index
- there is (or there's) with a compound subject whose first member is singular <there's an outhouse and a sump pump out back>: Stage 4
Key to the Language-Change Index:
Stage 4: The form becomes virtually universal but is opposed on cogent
grounds by a few linguistic stalwarts (die-hard snoots).
Garner's Stage 4 Analogies:
School-Grade Analogy: Grade B
Golf Analogy: Bogey
Olfaction Analogy: Vaguely odorous
Skill-Level Analogy: Amateur
Military Analogy: General discharge
Etiquette Analogy: Elbows on table
Traffic-Penalty Analogy: Warning ticket
School-Discipline Analogy: 1-hour detention
Moral Analogy: Peccadillo
Parliamentary-Discipline Analogy: Warning
As you can see, this is not quite standard yet, but Garner notes that using there with a compound subject is widespread nevertheless. He notes that purists still object to it, and to my interpretation, that it's technically incorrect. Therefore, while it'd be perfectly acceptable in speech, it shouldn't be used that way formally. Very careful speakers/writer's will object to this usage in writing.
Diana Hacker And Nancy Sommers also indicate that singular compound subjects take plural verbs in expletive constructions in Rules for Writers. They agree that in sentences beginning with there be--i.e., when the subject follows the verb in a declarative statement--the subject is plural if it's a compound subject, even if the first item in the list is singular, and therefore, it's got to take a plural verb
From Rules for Writers, 7th Ed.:
21g Make the verb agree with its subject, even when the subject follows the verb.
Sentences beginning with there is or there are (or there was or
there were) are inverted; the subject follows the verb.
There was were a social worker and a neighbor at the meeting.
The subject, worker and neighbor, is plural, so the verb that
follows must be were
Occasionally you may decide to invert a sentence for a variety of
effect. When you do so, check to make sure that your subject and verb
agree.
Of particular concern is are penicillin and
tetracycline, antibiotics.
The subject, penicillin and tetracycline, is plural, so the verb
must be are.
From The Chicago Manual of Style Online, 16th Ed.:
5.32Exceptions regarding pronoun number
There are several refinements to the rules stated just above: (1) When
two or more singular antecedents denote the same thing and are
connected by and, the pronoun referring to the antecedents is singular
{a lawyer and role model received her richly deserved recognition
today}. (2) When two or more singular antecedents are connected by and
and modified by each, every, or no, the pronoun referring to the
antecedents is singular {every college and every university encourages
its students to succeed}. (3) When two or more singular antecedents
are connected by or, nor, either–or, or neither–nor, they are treated
separately and referred to by a singular pronoun {neither the orange
nor the peach smells as sweet as it should}. (4) When two or more
antecedents of different numbers are connected by or or nor, the
pronoun’s number agrees with that of the nearest (usually the last)
antecedent; if possible, cast the sentence so that the plural
antecedent comes last {neither the singer nor the dancers have asked
for their paychecks}. (5) When two or more antecedents of different
numbers are connected by and, they are usually referred to by a plural
pronoun regardless of the nouns’ order {the horses and the mule kicked
over their water trough}. (emphasis added)
