Logitech K120 keyboard Linux Mint 17.2 Rafaela 64-bit Kernel Linux 4.3.0-040300-generic x86_64 MATE 1.10.2 Inkscape 0.91 r
A had this problem also and today unchecked Input devices > Use pressure-sensitive tablet(requires restart) The problem is gone!
Logitech K120 keyboard generic x86_64
Linux Mint 17.2 Rafaela 64-bit
Kernel Linux 4.3.0-040300-
MATE 1.10.2
Inkscape 0.91 r
A had this problem also and today unchecked Input devices > Use pressure-sensitive tablet(requires restart)
The problem is gone!