Carving has been said to be one of the WORST tools ever designed in any map making program

I have designed maps for quite a few games and in all the other programs I've used, I've never encountered anything quite so catastrophic as the carve tool for Hammer

I only use it you cut off pieces of a brush that I made a little to big and overlaps another brush.
I Strongly suggest that you learn to use the clipping tool, It's uses are innumerable and it's a lot more "Compile friendly"... Try Google for video tutorials, I found a few when I first started with hammer.