There is no denying the fact that there are many intransitive verbs with prepositions like the ones provided in the above question that can be changed into the passive. Please refer to page 11 of an advanced English grammar, with exercises (George Lyman Kittredge) stating "that an intransitive verb followed by a preposition is often used in the passive, the object of the preposition becoming the subject of the verb". He gave the following examples:
1- I was run over by the cart.
2- He was laughed at by everybody.
Moreover, in view of his statement, I don't think that when intransitive verbs are used with prepositions, they are considered transitive verbs.