I speed with impunity, trespassing means you've entered a station with no docking request, loitering for hanging around the wrong pad too long and will get fined for doing so.
Suggestions, practice docking faster, and make sure you request permission, or simply buy a docking computer module, and finally if speeding don't hit anything or let anything hit you...
Leaving the mail slot too slowly will trigger that warning too.
50-70 is slow enough for that to happen. I've had that more than once (usually when waiting for another ship to clear out), even before the game was released.
It's the only explanation i have for what the OP describes.
Since 100 m/s has been introduced, i've made sure to keep 90-100 when passing through the slot, and i've had no issues whatsoever.
If it's a bug, as the OP suspects, i would expect to have heard about it from others too.
A video would help to fully understand what's happening, coz i'm not really sure i do.