MVP Jython framework and edit grid

Introduction
I added a new widget to my MVP framework. It is an "edit grid" which allows modification data in the list directly (like in this GWT showcase) but allowing adding and removing rows dynamically.

This widget can be used when a number of fields is relatively small (containable in one line) and line editing is more natural then standard CRUD editing. Google App Engine live demo version is available here. Detailed description here, also source code and Selenium unit tests.
Problem
The main problem I found was to detect "the end of edit single line". There is no any direct "finish" button. This action is necessary to perform data validation and store data in persistence layer (assuming that one line reflects one record). The only solution I found was to discover the end of line editing after moving to the another line. In this case editing of the next line is suspended for moment and actions related to the last line are executed. If data validation fails then user is forced to return to the previous line and fix the data.
From that stems another problem. When user wants to finish editing he simply clicks "Accept" (or any other) button without moving to the next line. So it was necessary also to provide a way to declare which buttons requires validation of the last line.
 There are two ways of making data persisted. One is to persist data after any action relating to data change (after single column or whole line) or store all lines at the end of editing (after pressing "Accept" button or any other). In this case it is necessary to transport all data from the client to the server side. In order to avoid unnecessary traffic there is a way to specify which buttons trigger data transportation and which buttons do not. When data persisting is done at the end of editing there is a risk of losing all data just entered in case of any failure.
Next steps
I plan to use this widget in the JavaHotel application is several cases. The first case will be manually changing list price for reservation and bypass prices provided from regular price list.