I opened once a JPEG file from XnView MP 0.76 (same w/ 0.78) using gimp-2.8 (`gimp`is also available, but I use both gimp-2.6 and gimp-2.8, which executables filenames are installed by the relevant packages). XnView MP remembered that, good point, but now it proposes "gimp-2" in the list of applications (Open with..), instead of gimp-2.8.
My guess is that it's trying to name the application by removing the ending extension (.

like it's removing .exe on Windows, but this is definitely irrelevant in GNU/Linux, there is no real file extension for executables, what matters is how it is opened and by what.