returning in the middle of a using block

As several others have pointed out in general this is not a problem.

The only case it will cause you issues is if you return in the middle of a using statement and additionally return the in using variable. But then again, this would also cause you issues even if you didn't return and simply kept a reference to a variable.

using ( var x = new Something() ) { 
  // not a good idea
  return x;
}

Just as bad

Something y;
using ( var x = new Something() ) {
  y = x;
}

It's perfectly fine.

You are apparently thinking that

using (IDisposable disposable = GetSomeDisposable())
{
    //.....
    //......
    return Stg();
}

is blindly translated into:

IDisposable disposable = GetSomeDisposable()
//.....
//......
return Stg();
disposable.Dispose();

Which, admittedly, would be a problem, and would make the using statement rather pointless --- which is why that's not what it does.

The compiler makes sure that the object is disposed before control leaves the block -- regardless of how it leaves the block.