Parameter lost when calling a dll method using mozilla 1.8.1.18 on DMP

Question

This is a problem that has occurred after a Cisco 4400 DMP upgrade to Mozilla 1.8.1.18 (firmware release 5.3.5).

A C# method uses a command line (QueryString) parameter to invoke a method in a DLL using this variable as a parameter.

Here is the code snippet:

public string Get_Channel_Orientation(int channelId)
{
    ChannelService channelService = new ChannelService();
    return channelService.GetRootOrientation(channelId);        
}    

channelId is a QueryString parameter. This has functioned correctly until the browser upgrade. Now, what happens is the channelId value is always null. If you place a literal instead of the QueryString parameter such as:

  return channelService.GetRootOrientation(123);  

it works correctly even with the upgraded browser.

And even though it is null when passed to the Service method, if you print out the value of channelId to the console, it is correct (i.e. it is the value passed in the URL)

The situation seems impossible because it is server-side, and should not be affected by the browser version, but there is no other difference I can see between working and non-working cases.