If you check the source code it says:
/// The task is hidden. When the task begins execution, it runs in a hidden window.
Hidden = 0x200,
This supports my theory.
MS documentation is unclear: http://msdn.microsoft.com/en-us/library/aa381283%28v=VS.85%29.aspx what is hidden.
The thing is that with Task Scheduler 1.6.4 (and Hidden=false) the console window is hidden and with 1.7 (and Hidden=false) it is not hidden on the same machine. I only change the dlls. 1.6.4 is release compiled and 1.7 is debug compiled.