I actually tried "once" method. This seems faster i guess because i call these only once. I also dont see the point enabling/disabling them for every block.

But now i discovered that my vertex array version of DrawBlock eats up my RAM. And it gets very slow.
I will restore the DrawBlock from backup and will test if that removes the "memory eating". If yes, then i did something wrong (with sleepy head).

I thought its the map saving procedures that writes invalid map and when loaded damages memory somewhere etc. But the maps are binary equal to original editor maps.
Commented out "DrawBlock" and bug went away. So it is somewhere inside it.