Access 2010 - Using checkboxes for multiple selection in a multi-user environment

Forgive the novice nature of this question, I am not an Access expert.

A colleague has created a database for our team. Everything works great on the whole, the database is split out and we have our own frontend access on our PC's. Record locking does not seem to be an issue as we can all go in and amend records at the same time, change any fields, EXCEPT.. when we try to amend a multiple selection checkbox. We can be in entirely different records but when we try to select from the same checkbox field in different records, in any combination, we run into problems. It's as if the table where the checkbox selection is stored is locked?

Does anyone have an explanation that I can pass on to the colleague that created it, a solution does not seem to be forthcoming.

This is the only time that we have issues, all other fields are fine in multi-user environment. Please see screen grabs below.

Selecting checkboxes

Could not red the record, currently locked by another user

Thanks