Upon calling inventory or main menu the mouse pointers screen coords double (from centre).
Meaning that upon calling a new menu the start position of the cursor will be twice as far from the centre as it was when you left the previous menu.
My guess, it's an inversion of an intended 'cursor to centre function' which is called upon opening menus?, only it's moving the cursor in the wrong direction?
Hit Esc to call the main menu.
Move the mouse to as close to the center of the screen as you can.
Hit Esc to return to game and Esc again to re-call the menu.
Note that the cursor will have drifted a few pixels.
Esc twice
Note that the cursor will have drifted twice as far in the same direction
Repeat.
This may not seem like a problem: but on multi-monitor machines it can have the effect of moving the mouse cursor out of the DayZ window and into the window of another application, thus on computers running any form of X-mouse system (mouse over = focus) it immediately causes a loss of focus from DayZ and the associated task switching (Kind of a pain when you're trying to get a clip into your gun in a hurry, so you don't die).