My company has a web filter gateway that all external traffic must pass through.  This gateway requires AD authentication.  With our new Windows 8 clients, it appears that windows does a check for internet access, and when it encounters our gateway rather than the expected site, it launches Internet Explorer.  This happens each time a user logs on when the device is connected to our corporate network, but does not happen when on home networks (where there is no gateway).

Am I correct about my assumption that Windows is doing an internet connectivity check?  If so, is it possible to disable this check? 

Try adding this value:

reg add HKLM\SYSTEM\CurrentControlSet\Services\NlaSvc\Parameters\Internet /v EnableActiveProbing /t REG_DWORD /d 0

You need to disable proxy settings in IE when using from no gateway zone.

control panal-Internet Opetion- Connections-Proxy settings-(Automatically detect proxy settings)

If still issue. You need to check IP address and gateway on remote zone. and log on as local user not a domain user.

Sanjay