Photoshop :: Select Some Words / Change Color And Other Words Elsewhere Change Too?

I'm having in CS6..I have a text block with a couple of styles in it (headings have one look, body copy has another). Here and there, some words are on bold. When I select some bold words and change the color of them, some other bold words in some other paragraph also change color. Not all bold words... just some. The behavior is unpredictable, so the exact words that get changed will vary, but once it starts to happen it won't stop. When I try to manually fix the other words (hopefully I noticed them before my client!) and change them back to black, sometimes that change reverses the color on the original words too. Sometimes not; it's like the effect is sometimes two-way and sometimes one-way. It becomes a real logic puzzle sometimes, a maddening game where every change affects something else and you can't find the combination of actions that will do the simple thing you want.
 
I haven't noticed it happening with non-bold text, but that could just be coincidence.
 
When this happens, the only fix seems to be to rebuild the text from scratch in a new text box. (Copying it all and re-pasting it does not seem to work—unless possibly I paste into a different document entirely.)