I noticed this happening for the first time today so I don't know if this was an intended change, but I didn't see anything about it in the changelog.

Default leaderboard Variable leaderboard

Also, will it ever be possible to have times from different variables (by the same person) show up on the default leaderboard, like what currently happens with runs on different platforms?

Another minor, unrelated issue I found is this. I tried checking out several other games but I did not see any others that still have the 1970 date.

Yes that was a bug, thanks for catching it.

The option to show runs with different variables at the same time is something that should be added, but I can't promise when (it might have to wait until a complete update of how variables are implemented).

The 1970 date was due to the game being added before the add date was logged, it's been fixed to only show a date if a date was actually logged.