Thanks, I was really wondering what was causing this.

I had considered putting a standing order for hangar stay, but didn't get to test it - because I wanted to first solve that specific problem, which didn't happen with full empty schedules (and no interrupts).

Hello,

I wanted to learn train interrupts. So, I built a very small test track, in order to try a few things.
The track itself is a one-way loop, with four stations on it:

Test - Hangar
Test - D1
Test - D2
Test - Source

Test "Source" is on a side of the loop, while the three others are "in ...