Don't use sleep, it will not work. BA processes the Q2 trigger on each refresh so you need to let it do its work between refreshes.
See
http://gruss-software.co.uk/forum/viewtopic.php?t=3558 for an example that uses -3 to load the quick pick list then uses -5 to select the first market. It all happens in the Worksheet_Change event. It inserts -3 then sets a flag so that on the next refresh it knows to insert -5.
It doesn't seem possible that the results could reappear. Are you sure it's not the case that -7 wasn't processed at all?
the same happens if you manually delete A2:F1024.
This is not the same as using -7. -7 instructs BA to remove the list from memory. It writes it from memory on each refresh so blanking the worksheet will have no effect. Basically if after using -7 you can see that the results have cleared there should be no way for them to reappear because BA no longer has them in memory.