>Description:
	   There seems to be a problem in the mfs-layer which causes
	   a panic when for example pine messes with an mfs-mounted /tmp 
	   and one then tries to create a file in /tmp.

I wasn't able to reproduce this.  However...

   >How-To-Repeat:
	   [...]
		   While running pine will create a file on /tmp of about
		   4 GB in size (according to ls -l /tmp) this takes less
		   than a second and nothing seems to really be written.

This sounds like a symptom of an incorrect lseek() or ftruncate()
call.

It's not clear to me why it would cause a crash.