OK, finally I got some time to test this. I installed ADOM r52 in a different computer (which had never had an ADOM install before), with Win 7 64-bit, and could reproduce the bug.
But I think if you couldn't reproduce it, it probably was because my report was missing an important piece of information: it only happens in full-screen mode.
When the game is windowed, the cursor takes the form of a gauntlet, and it works fine, i.e. the character goes to wherever you point with the gauntlet's index finger.
However, when using Alt+Enter to enter full-screen mode (which is how I always play, that's why I took it for granted), the cursor takes the form of a blinking rectangle highlighting a map square (which is fine) but it's bugged as described: the PC often doesn't move to the highlighted square but to a contiguous one.