Hi londolozi,
I have investigated into this issue and found that the way this setting - "Clear previously imported cells" - works is as follows.
When you specify the range of selections and their custom cells, the program looks for them in the markets added to "My Markets". If it find a selection with a specified name, it
clears all cells that have been previously imported for that selection.
Which of course means that if you are trying to load a totally different set of selections, this will have no impact over the existing ones.
By the way, here is a quotation from the manual:
The box "Clear previously imported cells" will delete all cells that were previously assigned to the selections that you are trying to import.
So technically this is not a bug.
I now admit that the wording and the functionality of this setting is ambiguous and may mislead users. I do agree that a more straightforward behaviour would be just clearing all previously imported cells for all markets and selections whatsoever.