Unable to edit mailbox from imported website.

I import a website (hcadmin > migration > import website) and then I login as the webadmin for this website.
I then go to the domain > properties > Domain Services > Mail > Mailboxes
 
So there I get all the mailboxes that are connected to this domain and that are present on my mail server.
But when I select one and I go to "Edit Mailbox" I cannot click on Update Mailbox. I can click it, but there's nothing happening. So I can't update these mailboxes.
 
When I manually add a new domain to my HCpanel this is no problem, then I can edit all the mailboxes that have been added.
 
For the record: I'm using MailEnable mail server and I have the latest version of HC8 installed.
 
Is this a known issue and is there something I can do to fix this?

This problem could be due to a plan resource " TotalMailBoxSize"  if the plan which purchased by the webadmin includes limited Mailboxsize quota and at the mail server end if mailbox size is set with higher value or unlimited then such issue could appear in panel.
Just to verify set unlimited MailboxSize quota by editing the Hosting Plan under Reseller interface. If this doesn't solve the problem then I will suggest to open trouble ticket.