I have the same problem, tried with versions 3.6.5, 3.7.2, 3.8.2.
The problem happens when I trigger “reloadGrid” AFTER I've dragged any row. As JanM says, go to Demo Page/new in version 3.6/sortable rows, drag any row, then click reload, the cells are all disaligned.
There seems to be a problem with “table-layout:fixed” with Webkit browsers (Chrome), apparently it's not seeing the “jqgfirstrow”. There must be some javascript event making it load incorrectly, becaues in the DOM explorer in Chrome, I change all the tr rows to look exactly like they were before dragging (only removing zindex and opacity style from dragged row), but they still get disaligned.