Now, this totally baffles me.
I never thought that something might be wrong with plugins, so after peeking inside my script for setting things for configuring and compiling, I saw that I configured it with "--with-contrib-plugins=all" and I have all plugins active.
So I tried to disable them all, but CB then crashed n exit. So I disabled most of the plugins ( but left a few I felt are essential ) and everything started to work !
I could start empty project and import whole kernel sources into it ( some 20 k files ).
Funny thing is, code completion doesn't seem to be the culprit. Even more, even as I enabled all plugins back, emptied the project and reimported everything back, everything worked ! Import is slow, but once it is finished, it works. It seems that some of the plugins keep doing something in the background as CB starts eating some 5% CPU time for maybe 30sec every two minutes or so...
When starts, CB alone eats some 30MB. With all modules active that climbs to some 1.2G after importing whole kernel .
System works fine and not in any way pressed for memory - it seems that memory is swappable, so there seems to be no problem now...
Anyway, many thanks for the advice. It worked. I have no idea how, but the effect is certainly welcome ;o)