While editing my ship, sometimes the editor goes into a malfunctioning state, where the save button becomes unresponsive, along with the report bug button, and possibly some others. The color paint tool also becomes broken, not displaying any of the colors -- swapping between defaults still works, but custom pallete gets destroyed. I managed to create a subassembly of my ship in order to save its progress, and after deleting some recently added parts the editor became responsive again. I restored my ship from the subassembly, and even with the new parts I was able to save (and create this bug report).
I am not unable to reliably reproduce, but it has happened multiple times previously, at seemingly random times.