Key words here: "should not affect anything". You are correct, ampersands are a valid separator for query variables in URLs, as are semicolons. I'm simply stating that the way the TD tells IE which background image to use, the ampersand in that path could be an issue.
In fact, I guess I should have just done this before, but I just decided to test this and bingo it does appear to be the problem. I'll see if I can fix it for 2.6.