I know this is an old post, but I was having this problem as well. Here is how I solved it:

subGridRowExpanded: function (subgrid_id, row_id)
{


Thanks Oleg… I've saved a lot of time over the past few months thanks to your contributions.

I just downloaded 4.3.2 and everything is working fine in Chrome, however I am still seeing this “undefined” text problem in Firefox (3.6) and IE (all).

My code has the change that you suggested. I haven't been able to fix it so I reverted back to an older version.