Just an explanation on how it works.

When launching a DOS with the button, we simply use the inherited environment and launch the default DOS application. When launching the C compilation, we launch `finish_freezing' which modifies the environment so that it can find the C compiler. For that we have to use a Microsoft batch scripts which is supposed to extend the value of INCLUDE, not to replace it. So in theory the only bad thing that may happen is that the Microsoft headers are put before yours.

I know that in your case, the launcher sets the environment for C compilation, so you can edit $ISE_EIFFEL/studio/config/windows/msc/config.eif and set `smart_checking' to False, which would simply launch the DOS shell.

Let us know if this addresses the problem.