The article Advanced Load-on-Demand data retrieval through ISDataSourceControl support, in the WebCombo documentation, mentioned that we need to supply GetData and SelectCount method for the Load on Demand scenario to work, which will also work for ObjectDataSource. You could use stored procedures to retrieve the data in the GetData function.

Unfortunately, this method will require you to create schema for the datasource.

Further analysis of the issue has enabled our developer to discover the cause of this issue. It seems under GMT -5 Timezone, the issue you reported will occur. The issue occurs because the event has passed the Daylight Saving for that timezone.

A fix has been aplied in our nightly build, which could be retrieved here 

I have discussed this issue with the developer, this feature has not been supported in the current build of WebGrid 7.

However, the next build of WebGrid 7 will be enchanced to include this feature.

Thank you for the video, however I still could not replicate the issue using the live sample you shown in the video. I have asked my colleague's help to try to replicate the issue as well, however none of them successfully replicate the issue.

I have discussed this issue with the developer and they could not replicate the issue as well, our suggestion is please try to clear you browser cache in order to remove any previous version cached javascript.  

Update: 

The developer also suggest if the suggestion does not solve the issue please provide us with a virtual pc with your configuration so we could replicate the issue in our environment.

Attached is the modified sample with the workaround implemented. I did not encounter the issue you mention. In order to show WebGrid without the scollbar, I modify the select statement so it will only retrieve a single row.

I also modify the conditional, instead of comparing to the ClientHeight, it will now check against the WebGrid frame height. Since the original check is causing issue in Mozilla, the clientHeight will always has the same value as scrollHeight during WebGrid OnInitialize client side event handler.

In the original sample, it seems you are using master page in your environment, if possible perhaps you could create a simple master page that replicate the HTML structure in order to determine the issue.