There can be several reasons for this. Windows sets the default font for all dialogs based on your display and what the application has specified as the required font in its dialog definitions. There are two font names that dialogs normally use, "MS Shell Dlg" or "MS Shell Dlg 2", which map to different fonts depending on your version of Windows and your Windows language settings. Unfortunately, it gets even more complicated after that. See here
for a discussion on this.
That said, the only way to track down the cause would be to 1) have a small example script that I can use to reproduce the issue, and 2) use a 4k monitor, which I do not have at this time.