Error position top button after alter anchors

I have a TPanel with a TButton.

TPanel heigth = 77

Align = altop
BelvelKind = bkFlat or bkTitle or bkSoft

Tbutton property

top = 25

Alter property TButton

Anchors
akLeft = false
akTop = false
akRight = true
akBottom = true

After saving the form and closing the IDE form and reopening the form in the IDE, the top of the TButton changes to 21.
If it close again and open it will decrease the top by 4.

Thanks.