Sorry to necro this bug report, because for a long while I think this had been fixed (at least I didn’t have this issue with some of the previous models I’d worked on), however since the new Workshop Rig came out this bug seems to have resurfaced.
For the life of me I cannot get the weapon metadata to save properly, once I finish uploading and test it in-game, the gun is very far forward from my character’s hands. If I go back to the metadata screen it’ll show a slightly different but similarly too-far-forward position. If I just slightly touch one of the position values then it jumps back into the correct spot (temporarily).
Here are three examples, no matter what I try I cannot get it to look any different in-game even if I go nuts with the position values:
Better yet, here’s a clip of how easily reproducible this bug is. Just click “Done” after adjusting the weapon position, then “Edit” again and it’ll jump back to the broken position. https://www.youtube.com/watch?v=OvHKwK-OfIM
bump, 6 months later this bug is still around.. 
