Behaves inconsistently when `iskeyword` contains `?`

[qstrahl]

This may also apply to other punctuation characters, I'm not sure. To reproduce:

• set iskeyword+=?
• Perform <Plug>(asterisk-#) on a word containing ?
• The ? will break the word

Curiously, <Plug>(asterisk-*) does not break the word at ?. I think # should behave this way, too.