When opening a .sfz file, if one of its sample files is invalid, Polyphone displays an empty "Warning" dialog and hangs. While in this state, I was unable to take a screen shot.
After terminating Polyphone, screen shots worked again. Screen shots were disabled only while Polyphone was hung displaying the Warning dialog.
Steps to Reproduce
1. Find a sample file that is referenced by a .sfz file. Replace the sample file with a file that isn't a valid .wav file (I used a small text file).
2. Open the .sfz file in Polyphone.
Product Version = 2.3.1
Operating System = Windows 10.0.18362.959
Screenshot Software = Greenshot 1.2.10 Build 6 (64 bit)