I assume in GDL the texture is getting mapped per face? Once exploded to a morph, it reverts to a single UV map and even if you redefine each face, you are stuck with a single texture origin for the entire morph. Unless this was fixed since AC17, this also occurs with other primitives that you explode... Had a curved roof that changed pitch along it's length that when exploded to a morph became impossible to read strips of the same small portion of the original texture...
The imported object as GDL obviously maps one single complex map with all the pictures on it to each surface with extra insertion-coordinates and angles for this single picture. You can look at this picture in the imported library.
By converting the GDL to Morph, it looses this extra coordinates and simply puts this complex image without extra coordinates on each face - so this random surface appeares.
But - in Archicad - its manually possible to apply the insertion-point and angle for each texture , so the Data-structure in the Program itself must be there. Its just not implemented at exploding GDL to Morph. (dokumentation - rendering - set 3D-origin)
But in this case - such a complex picture cant not be set for each triangle per hand - you have no chance to find the right place for it.
So - Archicad should just copy the right texture-origin-coordinates and angles from the GDL to the Morph-faces automatically.
Its just laziness of the programmers in my opinion.. 😇
Thank you very much for sharing your experience with us! Checking the video, I think this error needs deeper investigation.
I would like to ask you to contact your local support by describing them the issue in detail, showing them this video and sending them all the necessary files (the GDL source file, an Archicad file in .pla format, etc.). Please mention which Archicad version and which update you are using and if you experienced this problem in previous Archicad versions.