I tested this bug today on two different accounts.
Account: BoredPandas (my collab account with my brother)
Account’s remix history: No remixes have been published on this account.
Projects remixed (in test): “we all matter,” published by tankt2016 on June 2; “Summer Pixel Art! v2.0,” published by Speeding Coder (my brother’s previous account) a couple years ago
Results: Both had a remix watermark
Account: tankt2016 (my main account)
Account’s remix history: Remixes have been published on this account dating back to 2016. I previously used this account to test the remix bug.
Projects remixed (in test): “Kaleidocosmos,” published by Valgo some time before November 2015; “Episode 7: Season Finale,” published by BoredPandas at the end of March 2020; “Bird’s Bakery: Banana Nut Bread,” published by BoredPandas in April or May 2020; “Summer Pixel Art! v2.0,” published by SpeedingCoder a couple years ago
Results: All projects, except “Summer Pixel Art! v2.0,” published by SpeedingCoder, lacked a remix watermark
Combined results: Half the projects remixed had a watermark. “Summer Pixel Art! v2.0,” published by SpeedingCoder, had a watermark on both accounts. Because that project had a watermark on my main account, tankt2016, what I had found before the bug fix (that didn’t work) was released — that once a user remixes a project and the project doesn’t have a watermark after being remixed, all projects the user then remixes will not have watermarks —doesn’t hold true anymore. I tested this bug with different projects prior to the fix though, so this might not have ever been true.