HTML Message Forward/Delete causes ACL problems

A couple of users we have regularly receive mail from particular newsletters that seem to cause crashes in the client. They are no longer able to do any functions within the client once they forward or delete the mail from their inbox. They receive a message “You do not have access to perform that operation” on any mail action until they completely close the Notes client and re-open it. It does not trigger on another machine opening the mailbox under different credentials, but an uninstall and reinstall has not fixed the problem on the user’s machine. Will attempt to try this on another machine with the user’s ID, but has anyone run into this before? When checking with the user’s credentials on that workstation, the ACL shows as “unsigned” even though using my credentials and checking the database on another system shows the ACL looks good. Why is an HTML mail triggering this problem? Has anyone seen this?