@ tagging does not work

Dear Podio,

This is second time that this function does not work. Someone on our team has added two new people into an item into a MEMBER field: https://podio.com/g8m8com/project-management2/apps/deliverables/items/371 
Added emails have created created PODIO accounts and have commented in the item.
I am main admin for PODIO system, but I am not able to tag these people.
The person who added them, she can tag them in the item.

We had this problem previously few weeks ago. Could you please look into this and have it resolved so we do not need to come back to this issue?

Thank you,

Peter