I cannot help you with the tiff weirdness. One of the reasons I switched from tiff to openEXR when exporting is the problems I had using tiff. Some stuff was rotated, or was visible in GIMP but was lacking in darktable. There was always something not quite right.
I also noticed that tiff exports, be it from GIMP or darktable won’t always be shown correctly in other image viewers (if it shows up at all). So I basically gave up on the whole tiff format…
About openEXR: Are you able to save to openEXR from darktable (not using edit with GIMP, but file on disk)?
One other thing when using darktable → openEXR → GIMP: When exporting from darktable I set the profile to linear Rec 709 RGB and the intent to perceptual This makes sure, on my side of things, that everything is the way it supposed to be.
I just made an exr in gimp and it came in to dt fine as a normal image import.
Just for the record, this is the first time I’ve run across this format it 25 years of digital imaging.
I’ve always gone in and out of Lr/PS via tiff export, but I was in the large format printing business, and it was a common format for RIPS and printing in general.
The tiff’s seem to be going out of dt and into gimp and back ok colorwise, and gimp picks up the sRGB profile of the dt file, asks if I want to covert to gimpsRGB (whatever that is) and I just say no.
I can live with the rotation, not an issue.
At the end of all this, everything gets exported to 100% jpg’s in sRGB space for upload to shutterstock.
I do anticipate that I’ll have others exporting as tiff for my (inkjet) workflow, which is ProPhoto or Adobe RGB, and the tiff goes into Photoshop on a VM Win for any raster work and printing via a Canon plugin. Does Photoshop open an EXR file?