This is starting to look like a bug in the Siemens PLC firmware v4.0.0.
A hotfix (Hotfix 1) for PLCSim Advanced V7 Update 1 was released 2 days ago. I am not sure which version of the firmware PLCSim Advanced used before the hotfix, but the KB says that Update 1 now uses firmware v4.0.4. After applying the hotfix, I can no longer reproduce this issue.
Another user has reported to us that updating their PLC to firmware v4.0.4 has also resolved the issue for them.
I'm still trying to confirm 100% that this is a bug in the firmware that is resolved in 4.0.4, but I am confident enough at this point to recommend updating. If you do update, please let us know how it goes for you.
Thanks!