See bug #150283 for the whole story.
Art Fore <art.fore@comcast.net> reported:
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I cannot print to "Letter" size media in ... Krita, I
have to reset the media size every time I open it.
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Set meddia size to "Letter" for my only printer, a Laserjet 2300,
in both the Yast printer dialog and in KDE print manager,
checked it with http://localhost:631/admin, but Krita still
comes up with "A4" in its dialog. I change that and save it,
print, which takes forever for a 5 meg file, and then
it is correct. I go out of Krita, back in with the same file,
print dialog is still set for "A4".
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It seems
1.
krita does not use as default media size
what is set for the print queue and
2.
it does not save the media size setting
made by the user.