I would advise that you examine the changelog of the OpenLayers map, because this is most likely an issue with event bubbling. Then the user resizes the RadWindow we need the mouse event, so the RadWindow scripts can resize the control. If the map consumes the event RadWindow will not be notified about it.
A quick search on the net seems to indicate that the fallThrough property now defaults to false, so mouse and keyboard events do not bubble anymore, so you may want to set it to true explicitly: https://github.com/openlayers/openlayers/blob/master/notes/2.13.md
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