MDI & MDI Child Forms Menu's in VB2005

Hi,

I'm using VB2005

I have an Mdi form and he have a MenuStrip in the properties I define the
AllowMerge=False
In the SubMenus of the MenuStrip there is some ShortcutKeys

I have also Child Form name Form1 and also he have a MenuStrip in the properties I define the AllowMerge=False
In the SubMenus of the MenuStrip there is some shortcutKeys

In the Parent Form and also in the Child Form I have some same ShortcutKeys, example: Ctrl+Z

I wrote the next code in the Parent Form:
For Each menuItem As ToolStripMenuItem In MenuStrip.Items
menuItem.Enabled = False
Next
'
Dim f As New Form1
f.MdiParent = Me
f.Show()

When I'm loading the Child Form from the Parent Form and when I'm pressing Ctrl+Z I get the result of the action of the Parent Form

Why?