The debug information I got from the console was this:
This looks pretty much like your example, I think.
All the HUD objects with which I have experienced this problem have been right at the edge of the screen (since this is where I put them to keep them out of the way), and the "shift" you describe does take place. Here is a part of a screenshot, showing the top-right corner of the screen, immediately after I have right-clicked on the square HUD object outlined in yellow, but before I release the click:
The picture does not show my mouse-pointer, but it was
repositioned over the central circle after the click, just as you describe, and as it should be. However, when I release the right-click, Inspect is instantly selected without my moving the pointer at all. When I have done the same thing with HUD attachments at the bottom of the screen, Detach was selected in the same way.
You asked about utilities that might be interfering with my mouse. I use a third-party Logitech mouse, with its standard Logitech Control Centre driver. I have not changed this recently, and I did not experience this pie-menu problem with the same set-up when using CoolVLViewer 220.127.116.11.
One final thing, and an apology. In my initial report, I forgot to include the Help/About information for my viewer: