I think the key might be here:
Code:
<00174> 0024094C P WM_SYSKEYDOWN nVirtKey:VK_MENU cRepeat:1 ScanCode:00 fExtended:0 fAltDown:1 fRepeat:0 fUp:0
<00175> 0024094C S message:0xBD04 [Benutzerdefiniert:WM_USER+47364] wParam:00000012 lParam:20000001
<00176> 004206AA S message:0xB016 [Benutzerdefiniert:WM_USER+44054] wParam:00000012 lParam:20000001
<00177> 004206AA R message:0xB016 [Benutzerdefiniert:WM_USER+44054] lResult:00000000
<00178> 0024094C R message:0xBD04 [Benutzerdefiniert:WM_USER+47364] lResult:00000000
<00179> 0024094C P WM_SYSKEYDOWN nVirtKey:'P' cRepeat:1 ScanCode:00 fExtended:0 fAltDown:1 fRepeat:0 fUp:0
<00180> 0024094C S message:0xBD04 [Benutzerdefiniert:WM_USER+47364] wParam:00000050 lParam:20000001
<00181> 004206AA S message:0xB016 [Benutzerdefiniert:WM_USER+44054] wParam:00000050 lParam:20000001
<00182> 004206AA S message:0xB03F [Benutzerdefiniert:WM_USER+44095] wParam:00000000 lParam:01CB8420
....
<00200> 004206AA R message:0xB016 [Benutzerdefiniert:WM_USER+44054] lResult:00000001
<00201> 0024094C R message:0xBD04 [Benutzerdefiniert:WM_USER+47364] lResult:00000001
First when you press ALT, the user message USER+47364 message is sent, with wparam=12 and lparam=20000001, which in turn generates another message USER+44054.
Afterwards, you press P. This is the moment that things get done, when the key goes down and not up. Of course this always ends up being a decision of the developer, but for menus for instance, they appear when the key goes down and not up. Anyway, when P goes down there is this message once again, USER+43764, this time with wparam=50.
Have you tried sending this message? If you have, have you also tried sending it first with wparam=12 (ALT down), then with wparam=50 (P down)?
I believe the developer might have implemented triggering the action on the equivalent of the OnKeyDown event:
if Key = 'P' then ....
Which leads me to another suggestion. How about sending the WM_SYSKEYDOWN messages yourself? The WM_USER messages might be just for other stuff, maybe the action you want is executed directly in the key down event, without resorting to any further message exchanges.