At the moment, Stadium and ManiaPlanet are in
beta, which means things are not finished yet. MX however, is not in beta, its a live site. If we allow people to upload envmix replays right now, then every Canyon record could be destroyed because the Stadium car is just usually going to be faster.
So therefore we can not just allow people to start uploading environment mixed replays. The measure we have put in place is temporary, to protect records hard fought on existing Canyon tracks.
We hope that Nadeo will be able to do something with the files so that sites like MX can correctly identify which car / title / environment was used. If they do this, we can then look at how MX will adapt to allow envmix replay posting.
Until then, and for now, we have to live with the restriction we have made.
* Autosaves are a side issue, if Nadeo update the way autosaves are saved, to be the same as how normal replays are saved, then autosaves would work again.