Tom,
further experimenting with the new maps have found two related problems, which happen using both Chrome and IE11. Looking at maps via the Maps Tab (which are impressively quick) if I untick date class bands from the marker style drop down box, a). the grid squares change colour / date class, rather than disappear, which is what some should do. So if i just leave the most recent date class ticked, all records are displayed as post 2010, even though many are from older date classes. And b). when some date classes are unticked, and I zoom in, display creates errors, with record grid squares only partially displaying and not lining up with the base map.
Leaving all date classes ticked and zooming in, the maps behave perfectly.
Andy.