Issues when updating FBX files with new UV data

I noticed, that Unity does not seem to import added UV Channels when updating an existing FBX Model in a project.

Example:

I created a model with 2 UV Channels (UV0 and UV1) in 3ds Max, export the FBX into my Assets Folder and use it in Unity...everything fine.
Later on, i realize, that i need another, additional UV-Channel, so i go back into 3ds Max, add a UV3 Channel and export the model as FBX again, overwriting the existing FBX in the Assets Folder.
When going back to Unity, i notice a short lag, telling me, that Unity is reimporting the FBX, but when i try to utilize the new UV Channel, it is still empty!

When i go on and export the model under a new name and do a clean first-time-import, things work as to be expected. All three UV-Channels are present and useable.

Has anyone encountered this issue? Is it maybe a known limitation or are there Workarounds?

In that regard, i also noticed, that Unity SEEMS to have problems, when adding new Submeshes to an already present FBX file (e.g. a FBX-file containing 5 cubes gets replaced with one containing 6). They sometimes don't show up either (but i have to verify this yet...)

 

you are limited to two (2) UV channels in Unity.

 

Just if someone runs into this: That's not true...you can use more than 2 UV channels....UV0 is Albedo/Main...UV1 is for Lightmapping (Static), UV3 is handled internally (Realtime GI, you can't access it), UV4 is available for whatever you want it to be...