>This is by design. Setting taborientation will reset the page height.

Why 257 ? height is set to 253:

PUBLIC oform1

oform1=NEWOBJECT("form1")
oform1.Show
RETURN

DEFINE CLASS form1 AS form

	Height = 300
	Width = 300
	AutoCenter = .T.
	Caption = "Form1"
	BackColor = RGB(0,0,255)
	AllowOutput = .F.
	Name = "Form1"


	ADD OBJECT pageframe1 AS pageframe WITH ;
		PageCount = 2, ;
		Top = 18, ;
		Left = 40, ;
		Width = 170, ;
		Height = 253 && ****** LOOK 

	PROCEDURE gotfocus
        CLEAR
   		WITH this.pageframe1 
   			? "height =",.height,"width =",.width
		ENDWITH
ENDDEFINE