I might have an explanation. Inside Qt, tabbing to an "anchor" (something that might have a context menu) gives me a X position that appears to be the top right corner of the box. The Y position is inside the box. Backtabbing in gives me an X position that appears to be the top left corner of the box with the Y position inside the box.
Theory: there are some situations where using tab-in, the position "misses" the corner because of rendered string length. I can imagine this happening if the screen scale is set to more than one hundred or if using a font where the size might need rounding when being rendered.
Questions:
- What is your screen scale?
- What font are you using?
- Does it happen if you use a fixed width font?