When loading EXR image we used to set the background to "Black" to display CandleGrass.exr-like images correctly. For some reason it doesn't work anymore. Krita loads EXRs with fully transparent background The bug is reproducible in krita/4.3 branch af77ed57599cab0e65a3b5470af666513f7f7bf0
I actually think you're going to need to do some archaeology here, because I remember seeing this change after a commit of yours that had, I think, to do with premultiplied alpha.
Git commit 7fc90d7614d20148bd78312acd1c94eab30e04c0 by Dmitry Kazakov. Committed on 20/08/2020 at 21:11. Pushed by dkazakov into branch 'master'. Fix errorneously set background color in EXR loading code M +0 -2 plugins/impex/exr/exr_converter.cc https://invent.kde.org/graphics/krita/commit/7fc90d7614d20148bd78312acd1c94eab30e04c0
Git commit 82c5624804f9df6309f8548892c01afad3f62d5c by Dmitry Kazakov. Committed on 20/08/2020 at 21:12. Pushed by dkazakov into branch 'krita/4.3'. Fix errorneously set background color in EXR loading code M +0 -2 plugins/impex/exr/exr_converter.cc https://invent.kde.org/graphics/krita/commit/82c5624804f9df6309f8548892c01afad3f62d5c