Minification is done using Google Closure Compiler which is quite memory eager (it does intensive computations on the generated code) and also really slow (and written in Java). I consider replacing it by another tool (UglifyJS) in next version which is a bit less performant concerning compression, but lightning fast and using far less memory.
However, I also watched it in task manager and it seems to give up while using only ~1080mb of code. With everything I had running, this was only ~50% of my available memory. I guess there is no way to prevent it stopping when memory usage gets this high if I still have memory available?