Could someone please test this to see if it's reproducible on another system? On my system (Vista Home Premium SP1, Dopus 188.8.131.52) it causes Dopus to predictably crash.
Step 1: Filter a list of files by extension using the filter toolbar control
Step 2: Click on top file and press F2
Step 3: Type a new extension (which would presumably exclude the file from the filter once the change is 'accepted')
Step 4: Instead of pressing enter, press the down arrow to go to the next file in the filtered list. At this point, on my system, the file icon for the file above is still visible, but the filename and file details become blank
Step 5: Press enter on the second file
Step 6: Click on the dropdown list on the filter toolbar control and select 'Clear Filters'
On my system Dopus will crash at this point.