BO4 - frozen browser after session timeout

Hi,

Using bo4 sp8.

we have a session timeout and idle document property timeout property set at 30 minutes and when expires the entire browser session is frozen.

Fine that session time out after this time, but would expect it just to say session time out and not just freeze the entire browser session.

IE and chrome same behaviour.

Any ideas why freezes entire browser session.

Thanks - screenshpt below.