Transportman opened the ticket and wrote:

It is a bit of a corner case, but when the platform length is changed while the train is in the platform it misses the station if the stop location is behind the train in the new case and goes searching for a new way to the station instead of just stopping and do its stuff. So if the train is set to stop at the near end and the platform is lengthened in that direction before the train comes to a complete stop, the train accelerates again to find a new way to the station (or stop in the middle and lengthen the station from the entry or shorten from the far end). It happens with both the YAPF and NPF pathfinders.

OpenTTD r25267 64 bits on Windows 7 without NewGRFs.

Reported version: trunk
Operating system: Windows

This issue was imported from FlySpray: https://bugs.openttd.org/task/5553