I have to patch the source code adding

if(ts.p.jsonReader.cell) cur = cur[ts.p.jsonReader.cell];

as we need to get the cells value from the fields dictionary.

===================================================================
— grid.base.js (revision 4833)
+++ grid.base.js (working copy)
@@ -508,6 +508,7 @@
addCell(t,row,cur[j] || ‘