Yes, APP can create proper 32bits HDR files for lighting, they are correct when using Simple blending (linear + diamond). The problem is that they are a bit blurry, but also you get a lot of overlapping blurred parts because the distorsion of some images are of course not 100% corrected.
The way I see it, Antighost is only Multiband with cutting. HDR output is Multiband and Fusion (and HDR ghosts, but that one works properly so I won't talk about it).
If you don't want to have overlapping parts of the pano that don't match exactly (even with all RMS below 5), which is what you get with Linear, then you HAVE to use Multiband with cutting, which is a blending mode that cuts the images in a smart way to keep the informations where it needs to be (and remove what shouldn't be there).
Multiband with cutting level -2 works great with pre-merged HDR files.
But it doesn't with bracketed exposures, it creates halos. The way I see it, it's like it's trying to blend the bracketed images in a certain way that is not linear (otherwise the same halos would also appears when stitching pre-merged HDR files). Why doesn't it apply the same blending everywhere, calculated from the reference layer?
So here, the output being fusioned or not fusioned, it doesn't matter. The issue I'm getting is only because of the Multiband cutting.
I have to redo all my stitching with pre-merged HDR files now (and we're talking about several dozens of spheres), while I already had done everything with the bracketed exposures while I was waiting to get a license, and I didn't check that the renders were 100% OK, the watermarks being on the images, I didn't pay attention to the halos. I take responsibility for my poor judgment
But that doesn't make me less disappointed, I really though APP was IBL lighting proof.
thank you both for your help. Klaus, you pretty much confirmed that we have to merge HDR files before, which is a cumbersome process. I already had to calibrate my raw files in ACR to get proper white balance, save them to TIFFs, then merge them to EXRs, and then finally stitch them. That takes a lot of diskspace.