Tested on Ubuntu 18.04 with Pinta 2.0 and the issue could be reproduced with Num Lock enabled (and xmodmap indicates that mod2 was set to Num_Lock). The commit mentioned in comment #12 fixed it in my testing.
Tested on Ubuntu 18.04 with Pinta 2.0 and the issue could be reproduced with Num Lock enabled (and xmodmap indicates that mod2 was set to Num_Lock). The commit mentioned in comment #12 fixed it in my testing.