I was having an issue where in CellEdit mode, cells that seemed to be blank were being marked dirty after leaving the cell. Turned out the cell contained an html encoded non-breaking space. I' still not sure where the nbsp is coming from so I can't say it's a bug.

I corrected by changing grid.celledit.js line 154 to this:

if ($.htmlDecode($.trim(v2)) !== $.htmlDecode($.trim($t.p.savedRow[fr].v))){

FYI – I'm using the latest 3.5 from github.