There is an "assign to contents" option when working with workbooks within projects--did you utilize this?
Also, are you certain it was working as expected in 8.0? I did not experience any issues when switching over to 8.1.
Permissions can be difficult to understand--I found this helpful when getting started:
Thanks Matthew - I believe I was guilty of not assigning permissions to contents as you pointed out.
I had been doing this for permissions on other projects but I simply must have missed this one.
Thanks too for the pointer to the related article
Happy to help!