NSDialogs in PortableApps.comInstallerCustom.nsh

I am trying to add a custom page to a PA.c generated installer (0.91.5) but when I get to the custom page the Back, Next and Cancel buttons are inactive and I have to use task manager to kill the install. Here is the code that I am trying this out with which is almost a direct copy from one of the example files included with NSISPortable.

!include LogicLib.nsh
!include nsDialogs.nsh

XPStyle on

Page license
Page custom nsDialogsPage

Var BUTTON
Var EDIT
Var CHECKBOX

!macro CustomCodePostInstall

	Call nsDialogsPage
	
	CustomCodePostInstallEnd:	
!macroend


Function nsDialogsPage

	nsDialogs::Create 1018
	Pop $0

	GetFunctionAddress $0 OnBack
	nsDialogs::OnBack $0

	${NSD_CreateButton} 0 0 100% 12u Test
	Pop $BUTTON
	GetFunctionAddress $0 OnClick
	nsDialogs::OnClick $BUTTON $0

	${NSD_CreateText} 0 35 100% 12u hello
	Pop $EDIT
	GetFunctionAddress $0 OnChange
	nsDialogs::OnChange $EDIT $0

	${NSD_CreateCheckbox} 0 -50 100% 8u Test
	Pop $CHECKBOX
	GetFunctionAddress $0 OnCheckbox
	nsDialogs::OnClick $CHECKBOX $0

	${NSD_CreateLabel} 0 40u 75% 40u "* Type `hello there` above.$\n* Click the button.$\n* Check the checkbox.$\n* Hit the Back button."
	Pop $0

	nsDialogs::Show

FunctionEnd

Function OnClick

	Pop $0 # HWND

	MessageBox MB_OK clicky

FunctionEnd

Function OnChange

	Pop $0 # HWND

	System::Call user32::GetWindowText(i$EDIT,t.r0,i${NSIS_MAX_STRLEN})

	${If} $0 == "hello there"
		MessageBox MB_OK "right back at ya"
	${EndIf}

FunctionEnd

Function OnBack

	MessageBox MB_YESNO "are you sure?" IDYES +2
	Abort

FunctionEnd

Function OnCheckbox

	Pop $0 # HWND

	MessageBox MB_OK "checkbox clicked"

FunctionEnd

Any NSDialogs wizards know what is going wrong?
Many many thanks