Giving up on x buffers - losing files

I've had this problem for a long time with 5.x, but it doesn't seem to  
happen that often. Today it bit me hard.

Sometimes, particularly after doing a lot of file writes (i.e. compiling a  
lot of ports, building world and mergemastering, etc), I get the 'Giving  
up on x buffers' message on shutdown, and my filesystems come up dirty  
when I restart.

This wouldn't be such an enormous problem, if it wouldn't always erase the  
files I changed most recently. The files are simply reduced to 0 bytes. My  
configuration files for Opera and KDE have been victim to this more than  
once (because Opera writes to the file on exit, for example), but today,  
it was /etc/master.passwd that was reduced to 0 bytes (because I had just  
changed something in it).

I understand that turning of write caching might improve the situation,  
but it also makes my system a lot slower, and I don't like that on my  
desktop system.

So, why does this happen? And how do I prevent it from happening? This  
definitely does _not_ sound like something I want my servers to do when  
5.x goes -STABLE.

Arjan