client script, 2.0, fieldchanged. When a vendor bill amount changes for a line, I iterate through all lines looking for the same PO# and update a field showing the $ remaining on the PO against all summed vbs. using commitLine to retain this value in real time. However, even when iterating backwards (line x to line 0) it still acts like I added a new line at position x+1, and users must click 'cancel' or face a 'please add an item' message. Should I be using a different trigger?

You can try seeing if forceSyncSourcing has any effect, but in my experience, nothing good comes from committing multiple lines in sublist related entrypoints