01-22-2017, 09:11 AM 
	
	
	
		Using Kubuntu 16.04 and Gimp 2.8.18 here, same as yours and as described never come across that before.
Reinstalling seldom does any good & since resetting tools does not work, try renaming your Gimp profile to ~/.gimp2.8-bak, Start Gimp to create a new default profile and see if there is a difference.
Are you using a tablet?
	
	
	
Reinstalling seldom does any good & since resetting tools does not work, try renaming your Gimp profile to ~/.gimp2.8-bak, Start Gimp to create a new default profile and see if there is a difference.
Are you using a tablet?

 

 
