Table header becomes FUBAR

Webix JS
1

Hello. Please check this snippet:
http://webix.com/snippet/32d56f17
Drag ‘B’ to ‘A’, then again - ‘B’ to ‘A’.

2

Fires:
Uncaught TypeError: Cannot read property ‘header’ of undefined

3

Automatic drag-n-drop of columns in a table with colspans is not supported.
If you need to have such kind of drag-n-drop, you need to catch the onBeforeDrop event handler and refresh the header in a necessary way.