Train stuck between waiting at station and working

[lukalyc]

I have a train stop for train refueling.
The train stop is hooked up to a train interrupt which activates if a trains nuclear fuel count is equal to 1, or the amount of rocket fuel the train has is less than 20.
Trains come to the refuel station, get fuel, but never leave, and instead get stuck between "waiting at stop" and "working".
This deadlocks the train until I intervene.
Expected behavior is that once the conditions to end the interrupt are met, the train moves on in its schedule.
This issue occurs for every train that comes to this stop.

[Loewchen]

Expected behavior is that once the conditions to end the interrupt are met, the train moves on in its schedule.

It does, and then the interrupt triggers again because rocket fuel is still below 20. NaB.