Is anyone able to help me with an issue that I can't seem to solve? I looked at this older thread but nothing seemed to apply or work.

The problem is that some users are unable to use the 'backspace' or 'return' keys when typing in to form text fields in protected forms.

The Word documents in use are either .doc or .docm files.
The documents are protected, for 'form filling' only, and they have text areas within them for users to type in to.
(The protection is enabled using "Developer" > "Restrict editing" > "Allow editing for filling in forms".)

It isn't happening to any one file in particular. We have many hundreds of these forms in use, and when a user gets this issue, it behaves the same on all the forms.

The issue affects one user on one machine. If they log in to another's PC it will work ok for them. Another user logging in to the fault-user's PC also can use the forms without issue.

Repairing office doesn't fix the problem.

Strangely the issue only happens to the occasional user now and then, but once it starts, there doesn't appear to be a way to stop it from happening until we have to resort to uninstalling Office and giving them a new user profile.

Any help would be very well received. Thank you.