Removal of ALL numbers (via backspace or otherwise) from a Number or Currency field on a table does not register in the model. This only happens when all numbers are removed, not when some of them are.

So, if I have a field ‘Amount’ and it contains 63 and I backspace it completely and leave it empty, the sum of the column will still contain 63 (presuming its the only row in the table) and the data in the model in Javascript will reflect that Amount contains 63.

However, if I only backspace the ‘3’, the sum and data will correctly be 3.