I just sent you the sources.

> The way it is now, it is normal you could have some situations like these.

Actually it's a completely normal situation. But VFP is unable to handle it normally.

> and not interfere with a user application. Or, at least, run it
> independently so it won't run into such situations.

They can not work independently, because VFP front-end displays state of the devices and works on OCX's events.