IDE 1.6.8 recompiling everything, every time

I've upgraded from 1.6.7 to 1.6.8 and found that a large project targeting a Mega2560 is recompiling every referenced file, every time. It used to only recompile the changed files referenced within the sketch.

I've uninstalled it, downloaded a fresh copy and reinstalled, with the same result. It's installed on 64-bit Windows 7 in C:\Arduino, and there are no spaces in the paths to any sketch or library.

Any thought, please? The slow build time is becoming a problem!

I have the same problem. Using IDE v1.6.8. It prints “Build options changed, rebuilding all” at the start, even though I’m not changing build options, and then recompiles every file all the time. Is there a solution?