Your instincts are right. From what I can see, the file ext-all.js has version 3.1 in Coldfusion 10, but version 4.1 in Coldfusion 11. Moreover, Coldfusion 11 still includes a large number of version 3.1 files. Not so developer-friendly of the Adobe Coldfusion Team. You have a right to expect backward compatibility, and should therefore report this as a bug.
Looking to the future, consider re-coding your grids using a Javascript library independent of Coldfusion, for example, JQuery. That way, you will avoid the whimsical version changes of Coldfusion's built-in Javascript.