I've tested this and it works:

The problem is caused by the igtbl_dispose method which delete the prototype properties and functions rather than just the local variables.

The fix for this is as follows:

Edit ig_WebGrid.js (found in the \Program Files\Symantec\Workflow\Shared\scripts\Infragistics\Scripts folder) and change the function igtbl_dispose(obj) as follows:

Change:

for (var item in obj) {

if (typeof (obj[item]) != "undefined" && obj[item] != null && !obj[item].tagName && !obj[item].disposing && typeof (obj[item]) != "string")

to

for (var item in obj) {
if (typeof (obj[item]) != "undefined" && obj[item] != null && !obj[item].tagName && !obj[item].disposing && typeof (obj[item]) != "string" && obj.hasOwnProperty(item))