Pre-populated "Qty" column on invoices acting up, Anyone else with this problem?

When I enter an invoice the Qty column sometimes has a prepopulated "1" in it as I tab accross, so if my invoice has 3 as quantitiy it now reads as "13" and I have to backspace to correct it, this seems to happen randomly is really annoying, I have used two different computers at two different locations to check if it was the interent or computer keypad but no and it happens randomly. Contacted QB but no help / solution offered, I think its a bug in the programme but its affecting my pace of data entry and I'm looking for an alternative package!