[mrcz]

it seems that Modo dosnt free the memory buffer after some functions.
After 3-5 consequent polygon reductions of a 900.000 polygon model Modo crashes always.

i used modo on a quadcore with 2 GB ram + 4 GB paging file.

Is that normal for Modo? may i'm dowing somthing wrong?

I have tried similar test to yours 1/ 2/ 3/ repeatedly in some scene. (all modeled inside Modo) Max Undo Level set to 10

Slow but No crashes.

My system is amd X2 + 4GB RAM + XP64. It was loaded another 1.5 GB application data in RAM, system was in usage couple of days without shutdown.
Modo is memory hungry. It eated 1.7 GB in my test, drop to 40MB after testing and deleting all meshes.

So it is no memory clearing case probably.

I suppose that you have Undo level set to 50 - which is default. Modo tried to save huge amout of undo data in memory and in this case your 2GB is not enough.

My suggestion is to lower Max Undo Level to 10 - minimum.