In Linelight for PC, it seems to be possible to collect keys for locked doors twice.

The bug allows to skip some screens that take longer as others when 2 keys are required to progress to the end of a world, but also to smuggle keys into upcoming riddles in order to skip them.

• In order for the Bug to work, key and door needs to be in different screens (loadingzones). This usually happens at the end of each world but also in some selective riddles in the game. Both Any% and 100% profit from this Glitch when it comes to the required riddles progression, yet with most optional yellow stars for 100% being locked behind a door where the key is in the same screen, the benefit for both categories is about the same.
• Keys can not be smuggled into upcoming worlds when kept at the end of the world. It just despawns and can no longer be used.
• The bug has only been sighted on PC yet. It is likely that the same works on Playstation 4, but unknown if it works on Android or iOS.

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The oldest documented case of this bug reaches back into June 2017 in this Steam Forum discussion: https://steamcommunity.com/app/469790/discussions/0/2333276539592194392/

The first documented use of this bug in a Speedrun is created by @Kynotzib and can be found here: https://www.speedrun.com/linelight/run/zx2w7lkm Example Timestamps (Video): 00:04:35 00:11:30 00:21:23 00:36:27 00:43:41 01:01:10