I came across a new word for me, 問{と}う (to ask, to inquire). I looked it up in the dictionary and it appears to be of a special class according to jisho.org. Other verbs listed under this category are 乞う,給う and 恋う.
I guess there might be some special conjugation rules that apply to this "u special class" of verbs, in a similar fashion to the special class of suru verbs (see this related QA).
By looking at some example sentences I found out that the conjugation indeed differs from that of regular u verbs in the particular case of the past form:
彼は僕にいろいろのことを問{と}うた (〇)
彼は僕にいろいろのことを問{と}った (×)
but I couldn't find more detailed information in how to conjugate this kind of verbs.
Besides conjugations, do the so called u special class verbs differ in any other aspect from regular u ending verbs?