Custom spawn locations default to 180 degree heading

1. Select a stock spawn location whose heading isn't 180 degrees and create a custom spawn location.
2. Relaunch the craft at the spawn you just created.
3. Whatever heading your craft is at at the time of saving is ignored in favor of a straight 180 degree heading upon spawning in that custom launch location.

This is troublesome especially for launch locations that don't have a spawn defaulted onto its runway (i.e Hypatch's various launch locations on his version of Earth)