Most laptops have a display switch key. This is sent in a variety of ways, generally either via the keyboard controller, via WMI or via ACPI. In Linux we take all of these events and turn them into KEY_SWITCHVIDEOMODE, making it easy to implement standardised behaviour.
This is, obviously, far too straight forward.
Microsoft, rather than introducing an input mechanism that allows all of these events to hook into the windows+p infrastructure, provide the following recommendation:
As documented in this Launchpad bug, vendors are starting to do this. It's been seen in HP and Dell machines, at least, and it's presumably going to become more widespread.
So, if your display switch button now just makes the letter "P" appear, say thanks to Microsoft. There's a range of ways we can fix this, although none of them are straightforward and those of you who currently use left-Windows-p as a keyboard shortcut are going to be sad. I would say that I feel your pain, but my current plan is to spend the immediate future getting drunk enough that I stop caring.
(The good news is that the same set of recommendations says that you can no longer put a Windows sticker on a monitor unless it has a valid and accurate EDID. The bad news is that that implies that you've previously been able to put a Windows sticker on a monitor without it having a valid and accurate EDID)