In the last version the method of calculating rent arrears was changed. As a result of that a previous feature is now redundent and has been removed.

Previously the rent period screen would allow you to edit the Rent Due This Period, Rent Paid, Extra Charges Paid and Amount Due this Period. Because the anount owing is now always calculated from the sum of the transactions, there is no point in editing the Rent Paid, because it will be ignored anyway. So to remove confusion this is now no longer editable, and is instead displayed as a label rather than a text box. The same applies to the Extra Charges Paid. The Amount Due This Period is also non-editable. The only field left as editable is the Rent Due This Period.