To address any possible question, I start with my specs
I have double CFed HD6950 2GB, installed on system with i7-2600k permanently turboboosted to 3.8 GHz, and 8 GB DDR3-1600. The OS is Win7 Ultimate x64 with Catalyst 12.3
The Game is with 1.9, DX11 update and hires textures installed and switched on

The first problem, that having 8 gigs of memory I run out of it pretty fast. sometimes I have barely enough time to get to the next checkpoint. It is manifested by windows message that the application uses somehow too much memory and needs to be closed. According to to task manager Crysis 2 uses "only" 1.3 GB at this point


The second that vertical lines transitions are not smooth.
For example sidestepping before a doorway will cause the doorway visibly distorted: the vertical lines becomes broken. This severely degrades graphics quality

I'm not sure of your first problem, but your second problem sounds like screen tearing. Turn on/off (opposite of the current setting) vertical sync and see if that helps.

yes you're right. turning vsync on would help. but oddly, switching to windowed mode also improves the situation.

Now I got further problem with vsync. In DX11 it caps FPS at 50 although i have 60 Hz pannel. with DX11 disabled it correctly at 60 FPS
also alt+Enter to windowed causes the game to sync at 60 FPS.

It's a bug with DX11, you have to disable and then re-enable VSync

Unfortunately, that doesn't help.
If it is abug, are devs going to do something about it?..

Unfortunately, Crysis 2 stopped receiving patches after the 5th one... I doubt there will be a new one, we can only hope.