I'm using photoshop CS5 and as you can see on the picture below, when I set my gridline to every 1 px, grid doesn't match canvas pixel size. I have never had this problem before and I have no idea how to fix this. Now I'm not able to draw sharp shapes using pen tool because even if I hold shift key everything gets blurry. If anybody could help me to fix this problem I would be grateful.
Does turning off OpenGL in the Performance Preferences and restarting Photoshop have any bearing on the issue?
The Rectangle Tool (with »Snap to Pixels« checked) works OK?
Are Photoshop and OS fully updated and have you performed the usual trouble-shooting routines (trashing prefs by keeping command-alt-shift/ctrl-alt-shift pressed while starting Photoshop after making sure all customized presets like Actions, Patterns, Brushes etc. have been saved and making a note of the Preferences you’ve changed, 3rd party plug-ins deactivation, system maintenance, cleaning caches, font validation, etc.)?
It's a strange one. I just took a look in CS5.1, same 960 x 650 px doc as before, set the grid to 1 px with 1 division and it definitely did not align with the pixel grid (similar to OP's image), which is consistent with my CS6 result earlier today. So I made a 4 x 4 px doc like yours and the grid did align. Switched back to the first doc to find the grid aligned. Now I cannot make a misaligned grid.