Hi Lucky,
I think there is a reason for this behaviour.
When count mode is 'auto', row count for each table is determined when table is rendered and does not change when browser window size is changed as tables are not re-rendered. You can force re-rendering of the tables by registering to window resize event, check sap.ui.Device.resize.
But you would have to consider displayed data in the table. For example. if there is a bound model and if user has navigated couple of pages forward, re-rendering the table to different number of rows, could lead to incorrect page/data being displayed. I have not tested this, suspecting some javascript errors in binding as there could be less number of table rows than data rows in model to bind. Alternative is to rebind the rows so paging is correct again, but users would have to start their navigation all over, which can be frustrating.
Hope this helps.
Regards
Raj