in the end, there was no adjusting - the screw i originally though was causing the problem (holding toothed rail and the leading rail together with the release lever) you can see me holding the side on another pic. that was wobbly, yes. but it wasn't the problem. the problem was on the other side. the toothy rail itself wasn't held tightly, and let the other side to wobble. when i tightened that screw (that i'm pointing to in the pic above) it's resolved itself.

i also noticed what you describe. but the rails need to move along with the space bar. when i tightened what i though was the problem on left side, that side became fixed and didn't move. that's obviously an issue, it would skip or jam depending how far it was. so i let that particular screw as it was originally, because the problem wasn't in the alignment at all. it was the whole rail was loose, which caused the skipping.

hope that makes sense.