Fbx import results different (broken) in 4.10 vs 4.9.2

Hey guys,
first actual post into the forum, and unfortunately it already seems to be related to bug report or feedback of a currently unexpected behavior:

Im just starting to learn UE and everything related to game Dev so I guess many times its just my inexperience with the whole topic. Tho im not new to CG as a whole. (Im a lead character TD for film vfx as a daytime job)
So im currently working on this little project game to learn all this and started with 4.9.2 very recently. I have my own rigs that I wanted to get into the engine, they have plenty of extra joints to improve deformation quality. That bit was pretty easy and the engine took my heavy rigs quite well. So on friday I bought this big movement animation package from the marketplace and retargeted it to my maya rig for re-export back onto my own skeleton (It needs to go through maya for all the auxiliary joints) All of that worked perfectly fine, I only did a quick automated batch retarget so most of the animations need some proper polishing by a real animator, but it worked for my purposes, everything went fine into UE4 and I was happy working on some character motion controller and all that fun… BUT NOW! …

A few days ago I switched to 4.10 and kept working on that… today I decided to edit my current jump loop animation as I was using the one from the UE4 3rd person project which didnt match my other animations. So I go to maya to grab one of the jump starts from the pack as a starting point … do my thing and set some keys … retarget and export the rig like I always do (wrote some python utilities to automate that) and try bringing that fbx back into UE 4.10. BUT!
Once inside the animation was barely there, some twisted joints and a skewed bind pose and some wiggle… thats all I got. Also the import took quite a bit longer than I was used to from 4.9.2. It displayed some secondary progress bar saying “importing animation track for [bone N etc.etc.]” And took about 25 seconds to import.
Heres where it gets crazy:

I thought it was some setting I forgot in my fbx export parameters in maya so I tried some different things. Apparently the first time I exported with the 2016 signature of fbx, surprisingly that did import into UE without crashing it, but the animation was nevertheless, broken.
So I tried it in 4.9.2 with the same file and surprise surprise, it imported perfectly fine and displayed correctly and the import was almost instantaneously. Then I went a little further and exported it back from UE 4.9.2 to fbx and imported that new export to UE 4.10. and now that one displayed correctly too.
Means that I have a workaround for now but its quite a strange thing so I wanted to report that here.

In case you want it to help you debug:
Thats a folder with both the original maya exported fbx and the fbx that I got from importing the maya one into 4.9.2 and then back out and then to 4.10.

Heres some images showing the difference between the correct and the broken results:

PS: sorry for writing the story of my life too, but I figured you might find it a useful fact to know how and where these fbx came from…
PPS: hm should’ve read the sticky first… sorry for that, Ill repost this in the answersHub bug report section.