We are using TMS Web Core 2.7.2.2. Sometimes more than one cell is selected in a TWebStringGrid. Looking at the code in unit WEBLib.Grids.pas, we found that the method TCustomStringGrid.GridChanged misses a call to RemoveSelection before setting FSelectedCell to nil:
if Assigned(FSelectedCell) then
RemoveSelection(FSelectedCell);
FSelectedCell := nil;