I tried that also … doesn’t help … and keeps on acting strange…
Now it exports a white background even though it should be transparent. (and I am exporting as PNG with default settings)
I am not a GIMP newbie … this is very strange…
Never had bug issues…
Works for me. This said the image is color-indexed (see title bar) so you are exporting a color-indexed PNG, which despite being part of the standard, is not always well supported. You can change your image to plain RGB mode (Image > Mode> RGB) to export a regular PNG.
Also, on my first export, it tried to export a JPEG and not a PNG (it also has JPEG-related “parasite” data(*)) so this could the remnants an attempt to export as JPG on your side.
(*) this is just the name Gimp uses for metadata it attaches to various things; image, layers, etc…
When you uninstall Gimp, your current Gimp profile is not removed, and is reused by a later installation. So:
You don’t lose any add-ons (brushes, patterns, scripts, plug(ins…) if you installed them properly (in your profile and not in the Gimp install tree)
un-install/re-install rarely fixes things (only the cases where the Gimp install itself is damaged, which isn’t that frequent).
There are however several places in the Preference where you can restore Gimp to factory settings.
In the dire cases you can just rename your profile. Gimp won’t find a profile, so it will recreate a clean one. You can then copy stuff from the old profile.
The indexed color mode is quite special. It is really designed to mimic GIF behavior. In particular it handles transparency differently, as an all-or-nothing characteristic. A side effect of this is that you get jagged edges:
This is because proper anti-aliasing relies on partially transparent pixels that blend with the background, producing the required intermediate colors: