Ajax events are not passed the proper variable value if the entity selected to be passed is not displayed in the grid. For instance, I have a grid that allows a user to select an image to attach to a document record. There are a couple hundred images to select from. The image Id is the value that I need to pass. However, if the id is not visible on the grid either the wrong value or no value is passed to the Ajax event.
I can understand that this may not be a bug, but instead may be a limitation of the grid. If this is the case, then you should not allow a user to select fields that are not in the grid to be passed as parameters to the Ajax event. This would also require the ability for the user to include the necessary field in the grid and either hide the column or set the column width to a very narrow value.