This happens randomly. Switching from PHP to CSS files (with several files open in windows/tabs) or opening CSS files, they open with no highlighting even though the bundle is set to CSS automatically. Happens mostly when Command+Option+Arrow between tabs or opening CSS files with several hundred lines. switching to another bundle and back to CSS fixes it.
If Textmate is open for a while (maybe 2 hours +) sometimes the text fields in the Find/Replace window become unresponsive (visually). The text in the search fields won’t update even though they are changing. Closing the search window and opening it again will show the changes but it’s only fixed by quitting and relaunching.
I can't reproduce these things at will, so maybe it’s something on my system and not a bug. Using OS X Mavericks with latest Textmate on Late 2013, 15" Macbook Pro.