OK,
I see:

- both in MM4 and MM5 the hotkey name is wrong, because for both Page Up/Down it shows Num 9/3 in Options > Hotkeys

- in MM4 it is only "cosmetic" issue, but in MM5 the issue is that the same action is actually performed for both 'Page Up' and 'Num 9'

Fixed the issues as
http://www.ventismedia.com/mantis/view.php?id=13954
http://www.ventismedia.com/mantis/view.php?id=13955

key logger works as expected on normal non numpad page up/down

Keyboard ID: 65658
Pressed Key: PRIOR
VKey ID: 0021
State Flags: 0002
HotKey: PRIOR
--------
Keyboard ID: 65658
Pressed Key: PRIOR
VKey ID: 0021
State Flags: 0003
HotKey: PRIOR
--------
Keyboard ID: 65658
Pressed Key: NEXT
VKey ID: 0022
State Flags: 0002
HotKey: NEXT
--------
Keyboard ID: 65658
Pressed Key: NEXT
VKey ID: 0022
State Flags: 0003
HotKey: NEXT

Looks like MM detect RAW key not representation with numpad.

Do you get same results with http://www.happymonkeying.com/eSupport/hotkey.zip

[quote]For me _both_ PageDown keys on my keyboard perform page down action (unless num lock is enabled) as expected.[/quote]

same here exactly, when I go Options/Hotkey and edit a hotkey with normal page down not on numpad it displays '3 (ZEHNERTASTATUR)', zehn means 10 and tastatur means keyboard so ZEHNERTASTATUR means numbad, when I press page down on numpad with numlock enabled it shows '3 (ZEHNERTASTATUR)', when I disable numlock it shows also '3 (ZEHNERTASTATUR)' so it shows '3 (ZEHNERTASTATUR)' three times no matter what.

Probably I still don't understand. For me _both_ PageDown keys on my keyboard perform page down action (unless num lock is enabled) as expected.

How does the Page Down on the num pad work for you? It doesn't move the tree down to the last node?

numpad is fine, normal page up/down is wrong

VK_PRIOR
0x21
PAGE UP key

VK_NEXT
0x22
PAGE DOWN

It works as expected for me.
When num-lock is on then they are 9,3 and when numlock is off then they works like PgDw/PgUp (moving the focus in the media tree)

yes

do you have numlock on?

page up/down key is mixed up with numpad9/numpad3