T junction rail.
Powered rails going in from the three lines. (not sure if needed, is what I did)
Normal rail for the switch junction in the middle of the T.
Redstone torch under the block with the normal rail to switch the junction, middle of the T.
At the top of the T, in the T junction, right next to the normal rail: Place a block.
When there is a rail on said block, the rail junction refuses to change state.
it does not matter what kind of rail is on top of the block, and it does not matter if it is powered.
Expected result: The rail junction switches normally even if there is an unrelated rail nearby.
Actual result: The rail junction refuses to switch state when there is a rail on a block close to it.
I testet it in 1.21.6 and 1.21.5
same result in both.
I made a video, it illustrate it best.
Although this may be intended, I was able to confirm it in 1.21.8:
[media]