[scala] how to stop recompile all scala files even there is no file has been changed?

Hi,

Firstly, thanks for this nice plugin, which is the main reason that I upgraded to IDEA 8.0.
 
it has bee a nice experience with this plugin. however, (1) it seems that all the scala files are recompiled when there is no file has been changed. is there a way to stop this as the compile time can be quite long for a fair size project.  In my case, it takes about 20 seconds.

Many thanks,
Andrew