The Observer block seems to detect an update from the back corner, the bottom redstone dust in 'Observer bug 2,' when redstone dust is placed adjacent to it in the positions in both images. However, this doesn't happen when repeaters face toward that dust, changing its direction. This strange update can make a clock where there shouldn't be one.

I didn't expect any update to be detected by the observer block when this happens. After all, the observer block only should detect one block.

Following the images, this can be reproduced easily.

Thank you.