Hi Jean-Marc Windholz,
A bit off topic, I noticed that you have added as a license developer the other Telerik account that you have. I would suggest that you submit support tickets/forum thread from the account of the license developer. This will allow us to recognize you as our customer and your support tickets will be reviewed according to the license that you have.
As to the question at hand, the menu item text is associated with the button text. This is why the menu item text changes whenever the button text changes. You can overcome this behavior by hiding the button element responsible for the text. In this way setting the button.Text property will change the menu item text, but this will not be visible in the button since this element is hidden. Then add your own text element and manipulate its text as needed. In this way you will have visible text in the button which will not affect the menu item text. Please find a sample project attached to this post.
I hope that you find this information useful. Should you have any other questions, do not hesitate to contact us.
the Telerik team
Q1’11 SP1 of RadControls for WinForms is available for download
; also available is the Q2'11 Roadmap
for Telerik Windows Forms controls.