I'm not sure what could cause this.
Is the grid's built-in functionality otherwise working after the asynchronous callback? If not, then a JavaScript error may have occurred that is preventing all JavaScript from running. If the rest of the grid's functionality is working, then I would next suspect there's something about how you're connecting your JavaScript function to the event handler.
My best advice is for you to submit a support request and attach a sample that we can run and debug that reproduces this behavior. A Developer Support Engineer will use that sample to determine what's happening and what can be done to resolve the issue.