Actually, the whole infotext code isn’t really made to work with inputs, although I do agree (personally) it should.
But the output is indeed, as you’ve noticed, not what you’d expect.
Unfortunately, nothing can be done about this unless we do some changes in the background.
It works with normal inputs though. So I’d advise infotext only to be used for norma inputs, and having those texts being entered separately outside the infotext (because in most cases, that info should be displayed somewhere, right?)