Cancelling a trip using API causes the trip to be re-assigned after less then minute

[wkulesza]

Expected functionality
Cancelling a trip using API command (cancelTrip) should allow to cancel an assigned trip and not cause autoassigner to autoassign it after 1 minute.
api/doc.html#/command/cancelTrip

Describe the bug
After cancelling a trip using api method, after less then a minute, this trip will get re-assigned

To Reproduce
Use api/doc.html#/command/cancelTrip to cancel trip. Observe as this trip gets autoassigned again.

Additional comments
Ideally, if api method would allow to explicitely setup expiry date of this cancellation. I.e. be default, it gets cancelled permanently until new gtfs-rt/gtfs appears. User can set expiry date (until when this cancellation is valid).