Hi,
I cannot reproduce this problem with PixInsight 1.8.5 on any of our working and testing machines, including Windows 10, 8.1 and 7 SP1. One of these machines is a Dell laptop with a 4K screen and Windows 10, where PixInsight works nicely with zero problems.
Try resetting all application settings. Launch the application with the Ctrl key pressed and answer yes to the subsequent confirmation dialog. This may fix these issues in case they are being caused by a wrong configuration. I have seen this happen in a few cases with users that had older versions installed.