[Lazarus] Selection issues in class derived from TCustomDrawGrid

[Werner Pamler]

In fpspreadsheet I am using a TsWorksheetGrid to display the contents of 
spreadsheet files. This grid is derived from TCustomDrawGrid, it gets 
all data and formats from the underlying TsWorkbook.

One thing which annoys me is that the grid can no longer select a range 
of cells once the goEditing option is set. An ordinary TDrawGrid has the 
same issue, but a TStringGrid on the other hand works perfectly. 
Therefore I guess that I forgot to modify a property. I looked for some 
time but cannot find the clue.

Any idea?