Sometimes one frame of the spritesheet is exported completely transparent

[Gnumaru]

Description

When exporting a spritesheet right after opening a new krita instance, it gets exported correctly, but if you close the file, open it again and export again, one of the frames will always get completely transparent, usually it is the first frame, but one time (only one) it was the second frame.

Reproduction Environments

I was able to reproduce the bug in these environments.

• Ubuntu 21.04, 64bit; Krita 4.4.5, 64bit, official .appimage downloaded from krita.org
• Ubuntu 21.04, 64bit; Krita 4.4.3, 64bit, community mantained flatpak build on flathub.org

Unreproducible Environments

These are enviroments where I was not able to reproduce the bug in any way.

• Windows 10 Pro 64bits version 20H2, build 19042.508; Krita 4.4.5, 64bit, official .exe installer downloaded from krita.org

Test Case

• close all running instances of krita
• (optional): clean your krita config folder by renaming "/home/user/.local/share/krita" to "/home/user/.local/share/krita.old", or "C:\Users\user\AppData\Roaming\krita" to "C:\Users\user\AppData\Roaming\krita.old"
• install a fresh plugin copy from Falano/kritaSpritesheetManager master branch
• Open up krita
• create a new 16x16 image (in fact the resolution doesn't matter)
• insert a key frame to the left of the first frame in the default paint layer
• paint something on the first frame
• paint other thing on the second frame
• paint other thing on the third frame
• paint other thing on the fourth frame
• save as a .kra file
• close krita (just to be safe)
• open up the .kra file created in the previous steps
• go to tools > scripts > export as spritesheet. Let every option as default.
• clik ok
• open the exported .png. It should be exactly as expected for a successful export.
• close the .kra document. Only the document, not the entire krita instance.
• open up again the .kra file.
• export again with the default settings.
• open the exported .png. It should always be missing one frame, almost always the first frame.

Details

Some details that may or may not matter to the issue at hand.

• I'm using the default ubuntu image, not any of the variants like kubuntu or xubuntu
• I'm saving the .kra in my home folder, /home/user.
• I'm exporting the .png to the same folder as the .kra file.
• My home folder is in the same file system as the OS root file system, not a different file system, nor a different physical/logical drive
• I'm not using LVM in the root file system
• My root file system is formated as btrfs mounted with compression=zstd:1
• I wasn't able to test a flatpak build with version greather than 4.4.3 because 4.4.3 is the latest verion on flathub.org
• I wasn't able to test the 4.4.5 snap build from snapcraft.io because I wasn't able to enable python plugins. The plugins section on the configuration window is just missing.
• I wasn't able to test the 4.4.3 apt build from the default ubuntu repository because I wasn't able to enable the plugin. Whereas the snap build doesn't show the plugins section at all, the apt build does show the plugin section, but it comes completely empty for some reason, even though there are plugins both on "/usr/share/krita/pykrita/" (where the plugins installed via apt should be) and on "/home/user/.local/share/krita/pykrita/" (where user installed plugins should be).

Notes

• for anyone wondering where the krita folder is on the flatpak and snap builds, on flatpak it is "/home/user/.var/app/org.kde.krita/data/krita/" and on snap it is "/home/user/snap/krita/64/.local/share/krita/"
• Instead of oppening new issues I would like to mention that, sometimes, the export window does not close after finishing export. Also, It would be nice if the default spritesheet name would be the same as the current document name.