Here is an additional screenshot:

- darksithlordcaret.png (33.99 KiB) Viewed 4907 times
Yes the caret functionality works fine. This is a redundant fixed black rectangle that only appears when HxD is launched with a file path parameter. If a file is opened using any other method it never appears, although the caret functionality always works correctly.
This appears to be some sort of drawing bug or initialization issue. I haven't been able to test whether this only occurs on Windows 7 or not but it is possible the current code sets up the caret rectangle (GDI functions?) in a way which fails under specific versions of the OS. The only thing I can think is perhaps there is a missing DeleteObject() or mismatched BeginPaint() EndPaint() calls?