Screenshot 1
Screenshot 2
When hovering over the chain signal, only one rectangle for train positions is indicated, which means that a 2-long train shouldn't be able to fit without clipping into the next block.However, when a 1-1 train stops there, it just barely fits, leaving the next block unoccupied as shown in screenshot 2.
The train got there in automatic mode so it's properly aligned, and I've checked with different signal types, fuel sources and train composition (loco/wagon, wagon/loco, loco/loco) just to be sure.