The issue is better explained here syl20bnr/spacemacs#2707.

It basically seems to only happen in some terminals, but it did use to work in both terminator and cool-retro-term. I am in the process of trying to revert to an older version but I am not sure if it's easy to do.

Unfortunately, I do not update spacemacs that open, so I can't tell you an exact time this was introduced, I'd say it worked about 2 weeks ago.