[SOLVED] 3.6.7: No space after colon (:) in post title

I've just updated, and now the space after a colon in my post titles has disappeared.

In the post editing window, it looks like this—


When displayed, it looks like this—


UPDATE: I've just realized that it's not just colons, and not just in post titles. In the posts themselves, and in my sidebar widgets, there are no spaces after commas. The spaces after full stops, however, display correctly.

Ideas?

Eric