I had previously uploaded a game version 2.14.something using butler.

I am now working on a new version of the game (v3.0). I used butler to push a demo to the game page.
The file has a different name. In the past that meant it uploaded the file as a separate download option.
But now it has overwritten v2.14.

Am I doing something wrong? Or have you guys updated this behavior?
How can I use Butler to have both files available at the same time?

Pushing to a channel will advance that version, there’s currently no way to split a channel. If you want to have a separate downloadable archive of a version available then I recommend upload it as a separate channel.