My PC/AT originally came with a Model F keyboard. I've been using it with that since I got it.

But I also own a Model M keyboard, from the PS/2 era. I have a PS/2 to AT adapter so I thought what the heck, I'll try hooking this up to the AT.

So far it works great, with one exception.

The arrow keys work strangely. You cannot use them in combination with the "home", "end", etc. keys to highlight text. And you cannot use them to navigate back through text you've typed in the command line, as the left arrow acts the same as the backspace key.

But if I use the arrow keys and "home", "end", etc. keys in the numpad, *then* it works.

What gives? Is there some incompatibility I didn't know about here?