Consulta sobre userform abiertos en excel

Buenos días
Tengo una consulta con los userform en Excel, y es que tengo unos formularios que funcionan bien en un determinado libro de Excel, pero si abro otro libro de Excel
el userform se abre en el nuevo libro.

Alguien sabe cómo hacer para que el userform se ejecute en un solo libro?

Nota, utilizo este código:

Option Explicit ' Declaración de variantes para los botones de maximizar y minimizar
Private Declare Function FindWindow Lib "user32" Alias "FindWindowA" (ByVal lpClassName As String, ByVal lpWindowName As String) As Long
Private Declare Function DrawMenuBar Lib "user32" (ByVal hWnd As Long) As Long
Private Declare Function SetWindowLong Lib "user32" Alias "SetWindowLongA" (ByVal hWnd As Long, ByVal nIndex As Long, ByVal dwNewLong As Long) As Long
Private Declare Function GetWindowLong Lib "user32" Alias "GetWindowLongA"
(ByVal hWnd As Long, ByVal nIndex As Long) As Long Private Const WS_MINIMIZEBOX As Long = &H20000
Private Const WS_MAXIMIZEBOX As Long = &H10000
Private Const GWL_STYLE As Long = (-16)
Private Const WS_SYSMENU As Long = &H80000 'variable para ocultar el botón x

Private Sub UserForm_Initialize() ' Declaración de variantes para los botones de maximizar y minimizar
Dim lngMyHandle As Long, lngCurrentStyle As Long, lngNewStyle As Long

If Application.Version < 9 Then

lngMyHandle = FindWindow("THUNDERXFRAME", Me.Caption)

Else
lngMyHandle = FindWindow("THUNDERDFRAME", Me.Caption)
End If
lngCurrentStyle = GetWindowLong(lngMyHandle, GWL_STYLE)
lngNewStyle = lngCurrentStyle Or WS_MINIMIZEBOX Or WS_MAXIMIZEBOX

'SetWindowLong lngMyHandle, GWL_STYLE, lngNewStyle
Dim hWnd As Long 'para ocultar el botón "X"
Dim lngWstyle As Long
'Localizar la ventana del formulario
hWnd = FindWindow(vbNullString, Me.Caption) lngWstyle = GetWindowLong(hWnd GWL_STYLE) 'Borrar el botón X SetWindowLong hWnd, GWL_STYLE, lngWstyle And (Not
WS_SYSMENU)
'Dibujar de nuevo la barra
DrawMenuBar hWnd
End Sub

Private Sub UserForm_QueryClose(Cancel As Integer, CloseMode As Integer)
If CloseMode <> vbFormCode Then Cancel = True 'para deshabilitar el botón salir
End Sub

De antemano, Gracias