Screenshot Plugin Issue

Occasionally when I go to make screen shots of a matroska file (.mkv) I’ll click the “save all” button and it will download but at the last minute it will change from the title of the video file and the .tar extension to “action.php”. It doesn’t do this all the time, just on and off with the same video file(s). For example a day ago it was doing this behavior of changing to action.php for every video file and now it seems to work. What’s causing this and how can I fix it?