I have chopped it down to a simple example. If you run the page below in IE8 there is a strange behavior in the grid. When clicking a cell or double clicking to edit, the cell border changes and is no longer aligned with the column. Changing the DOCTYPE to:
fixes the issue but my understanding is that the grid should function correctly with the XHTML doctype.
Trip Scheduler
This bug was confirmed and fixed. Fixed file will be included in the next dhtmlxGrid version. If you need changes immediately please contact support@dhtmlx.com and provide you ref. ID.