Ver 1.08, but likely present in all future versions

When you place a RLC on the ceiling, the visual colours do not match the logical colours for the IO. 2 colours get swapped. Likely just a visual glitch caused by flipping the texture for use upside down, but it causes confusion with programming.

To replicate: put a RLC upside down on a ceiling, run a bit of redstone out of each side with the pen. Use the RLC to output on each of the IO ports, and see what lines up and what doesn't.

Hi aurum, aye I have seen the issue a short time before and have actually fixed it in v1.2.17. Just didn't get around to port the fix all the way down to 1.16. Hope that I get to tackle that in the next week or so. It's (as you already reckoned) a swapped model.
Cheers,-

Excellent. It's not a big deal once you know about it, just figured I'd let you know. That is definitely the kind of bug that is hard to catch in QA :)

Hi again, just wanted to start porting down the fix and had to realize that I was waffling bollox - the fix for 1.16 is already pushed:
v1.16.5-1.0.9 (https://www.curseforge.com/minecraft/mc-mods/redstone-pen/files/3983482). Sorry about the pointless delay there ;/.