I am not able to reproduce this issue. Resizing images and using the paintbrush tool works without crashes in my testing.
Using Pinta 1.6-2 from stretch, -- System Information: Debian Release: 10.0 APT prefers testing APT policy: (500, 'testing'), (1, 'unstable') Architecture: amd64 (x86_64) Kernel: Linux 4.19.0-5-amd64 (SMP w/4 CPU cores) Kernel taint flags: TAINT_CRAP Locale: LANG=en_NZ.UTF-8, LC_CTYPE=en_NZ.UTF-8 (charmap=UTF-8), LANGUAGE=en_NZ:en (charmap=UTF-8) Shell: /bin/sh linked to /bin/dash Init: systemd (via /run/systemd/system) LSM: AppArmor: enabled Versions of packages pinta depends on: ii gnome-icon-theme 3.12.0-3 ii libc6 2.28-10 ii libcairo2 1.16.0-4 ii libgdk-pixbuf2.0-0 2.38.1+dfsg-1 ii libglib2.0-cil 2.12.45-0xamarin14+debian9b1 ii libgtk2.0-cil 2.12.45-0xamarin14+debian9b1 ii libmono-addins-gui0.2-cil 1.0+git20130406.adcd75b-4 ii libmono-addins0.2-cil 1.0+git20130406.adcd75b-4 ii libmono-cairo4.0-cil 5.18.1.3-0xamarin3+debian9b1 ii libmono-corlib4.5-cil 5.18.1.3-0xamarin3+debian9b1 ii libmono-posix4.0-cil 5.18.1.3-0xamarin3+debian9b1 ii libmono-sharpzip4.84-cil 5.18.1.3-0xamarin3+debian9b1 ii libmono-system-core4.0-cil 5.18.1.3-0xamarin3+debian9b1 ii libmono-system-xml4.0-cil 5.18.1.3-0xamarin3+debian9b1 ii libmono-system4.0-cil 5.18.1.3-0xamarin3+debian9b1 ii mono-runtime 5.18.1.3-0xamarin3+debian9b1 pinta recommends no packages. pinta suggests no packages. -- no debconf information