Hi! :-)
When executing a BAS file, it's opening the interpreter and starts running the file.
If the program cursor is inside an INPUT box waiting for the input and press alt-tab, when (with alt-tab) returning to the program, the focus on input box is lost and you have manually click with the mouse inside the box.
Pressing the TAB key, don't help.
On Win7 x64 GR.
This has all been re-implemented in the updated SDL version