From Amir:
If I log in as "joe" (who is an editor) and activate content I am unable to see it in the Inbox, which is good. Then I log in as "melinda" (who is a publisher) and I can see activation requests from "joe" - excellent. However, any action from melinda (proceed, cancel, reject) throws an exception (see attached)...

Indeed. This seems to be because openwfe is unable to decode some attribute of the workitem properly; apparently it'd be the user's permissions, wrapped in a LongAttribute, but with a java.lang.Integer value. Seems to be a very similar issue than with MAGNOLIA-1392