FileMaker maintains the current sort order when you edit a field referenced in that current sort order. As a test, select Sort from the records menu and check to see what fields are specified in that sort order just before you start editing records. FileMaker will maintain that sort order, moving the record you edited to a different location in the found set if a value in one of the fields specified in the sort order was modified. This appears to be what you have taking place here. Many have complained about this "auto-sort" and have requested that FileMaker Inc. at least give developers the option to disable the auto-sort for specific layouts. Keep in mind that a sort order can specify multiple fields and that editing any one of the fields specified in the sort order can result in the record "jumping" to a new spot in the sort order in order to maintain the sorted order of records.
As described in the thread where you first posted, this auto-sort can be temporarily disabled by editing your data while a script is paused. When a script is paused, the auto-sort won't kick in until you continue or halt the paused script.
Thanks, the documentation could be a little clearer that sorts remain active indefinitely. I tried turning off sorts by following a sort by another that sorted on nothing, but that didn't seem to have any affect. It is odd that there is no way to turn this off.
You have the option to Unsort the records. That would also disable the sort, but it also re-orders your records into the order they were originally created or imported into the table.