Channel manager sometimes logs errors to javascript console

The channel manager sometimes logs the following error to the javascript console:

this.config[col] is undefined
return this.config[col].dataIndex;

Steps to reproduce:
1. open the channel manager in Firefox 6
2. open the console in Firebug
3. move the mouse pointer quickly over the grid for a while

The error will popup a number of times after a few seconds of moving around the mouse pointer.