Is this related to the issue mentioned here?
Thanks for your suggestion, but I checked that too. It's not a class in a class in my case, not a class I created at all actually. The PropertyBag class is created by EPiServer, and when I decompile the related code I can see that there is actually a condition for PropertyBag objects that get their store name in a different way. So it seems to be meant to work, but it doesn't for me.
I just tried it out, and got the same result. It's a bug, and I'm currently looking for a workaround for the propertybag, but I can't find any right now.
I created a PropertyBag with just a boolean value, and got an exception trying to save it using PageObjectManager. Is that not possible? The exception message is:
Invalid name format for storeName. Only characters a-z, 0-9, '.', and '_' are allowed for security reasons. Name:storeName, value PageObject.CommentStatus.f794edf7-fa14-463f-881c-02839545180f.