I have increased the priority of RF-37 up to Critical.
This kind of behavior is usual for situation when the input field is located inside the re-rendered zone. It happens because the DOM node is replaced (removed and added) and browser just loses the node where the focus was in.
If dataTable has no ajaxKeys defined OR ForceRender listener defined, the whole table with be re-rendered. This causes the focus losing .
However, in your case, you have a listener. So, it was a bug.