handcrafted: We are experiencing an issue since you created the July version.
Are you working from a custom screen, I just tried to reproduce this error through my stock screen and I wasn't able to. Could you let me know exactly what steps you are taking?
On my account I went to Field Service Center > Customers and selected a customer with a few work orders. I clicked the last tab section for Activities & Work Orders then clicked Edit... on the first work order. I made a slight adjustment to the work order instructions then clicked save & close. The work order closed and I did not receive and error.
I might be missing a step here so please let me know if your process was any different.
~C