Are you modifying the record in code? That over-rides the Allow Edits restriction until the record is saved, then the property will be reset. However, I don't know if that applies only where you have set the property in design, or if it also applies to when you set it in code. If you don't need a form recordset to be editable at all, it's easier to just open it with a snapshot type recordset.
If it happens throughout the db and it's a new behaviour, then maybe it is corruption as suggested.
The more we hear silence, the more we begin to think about our value in this universe.
Paraphrase of Professor Brian Cox.