Punctuation in item descriptions gone Wonky

I’m moving around some products into a different category. Everything moved fine except for two items, which keep giving me a 404 error when I update with the new category.

Okay, fine, so I tried to simply recreate those items from scratch and assign them to that category right off the bat. 404 error again.

Really weird, because I’ve been adding things and moving things since before the last update with no issues.

So I tried to make a new test product from scratch. I’ve narrowed it down to being picky about punctuation. Here are some examples:

This sentence works:
The ultimate dog sports t-shirt. Sometimes Q-Less, but always having fun

This sentence does not:
The ultimate dog sports t-shirt. Sometimes Q-Less, but always having fun.
or:
The ultimate dog sports t-shirt. Sometimes Q-Less, but always having fun!
or:
The ultimate dog sports t-shirt. Sometimes Q-Less but always having fun!
or:
The ultimate dog sports t-shirt. Sometimes Q-Less, but always having fun. But

I also tried copying and pasting the “approved” sentence ten times (to make a big block of text) and that worked fine.

I get an Error 404 every time for the other sentences. It’s driving me batty. Help please!