I've had a few strange things happen when I add an adjustment layer to my timeline. On one occasion I added a blur to the adjustment layer and when I switched from video to waveform in the program monitor the whole project froze up. I had the same issue when I added a fade up to the adjustment layer (CTRL D). If anyone has any idea how to fix this I would be very greatful..
I'd start by cleaning your cache and perhaps trashing your prefs. Beyond that, if it's a really big project with tons of clips, I'd say either try and clean out what you're not using or add a bunch more RAM to your system if possible.