Sendkeys and Numlock: a mechanical issue

Greetings. I have a swithbox for switching between 2 PCs that share a single keyboard and mouse. My old switchbox used ScrollLock to soft switch between the two machines. It had to be replaced and my new switchbox uses NumLock to soft-switch. Now, when I run a macro using SendKeys the computer switches me between the macines by itself because SendKeys causes multiple NumLock flashes. Does anyone know why NumLock flashes with SendKeys and how to get around it?

Thanks,
--Doug