Hi global_ant -
we did receive a similar report regarding the Optional eBay Gallery images, however we have not been able to reproduce the issue as described. Both scheduling and saving listings are keeping that selection, so it is unclear what may have occurred. I suggest that you try clearing the cache of your browser and then logging back in to your account to try again.
Should you encounter this again with either Saving or Scheduling a listing where the Optional eBay Gallery Images box becomes unchecked, please file a support case letting us know the steps you are taking as well as your browser and operating system so we can look into this further.
- Craig