xl03/XP

The worksheet's rows are contiguous (1-8,724).
When I attempt to sort, it selects the cells starting in row 5693.
It is the same effect as if there were a gap and the active cell were in the lower portion of
the sheet.

If I copy all cells to a new sheet - all is well.
If I copy the sheet ("Move/Copy") it fails on the new sheet.

If I insert rows and select a cell in the upper region the sort command still selects the bottom
region.
There aren't any hidden rows etc.

Using VBA the CurrentRegion is correct as is the UsedRange.

As noted I can get around it by copying the cells to a new sheet, but it's got me "bugged".

Any hints?
--
Regards
Rob