I have a Client Script running under PageInit that adds a line to the start of a transaction:

function pageInit(context) {
		var currentRecord = context.currentRecord;
		var checkLine = currentRecord.getSublistValue({
			sublistId: 'item',
			fieldId: 'item',
			line: 0
		})
		log.debug('sublistChanged','checkLine: ' +checkLine);
		if (checkLine != 8957) {
			currentRecord.insertLine({
				sublistId: 'item',
				line: 0
			})
			currentRecord.setCurrentSublistValue({
				sublistId: 'item',
				fieldId: 'item',
				value: 8957,
				fireSlavingSync: true
			})
			currentRecord.setCurrentSublistValue({
				sublistId: 'item',
				fieldId: 'rate',
				value: -10,
				fireSlavingSync: true
			})
			currentRecord.setCurrentSublistValue({
				sublistId: 'item',
				fieldId: 'custcol_sgl_reason_for_adjustment',
				value: 20,
				fireSlavingSync: true
			})
			currentRecord.commitLine({
				sublistId: 'item'
			})
		}
	}

This has worked successfully for a number of months, but recently the script has started adding the line at the end of the transaction.