macro's name changed. prepended with worksheet's name

[nbaa67]

Hello
Has someone already experienced the following problem:

Suppose I have a button B in worksheet W which is assigned macro M.

At some point (don't know exactly when or how) the button B is no more
assigned M but W_M. The macro is prepended by the worksheet name.

Other case, the button B is assigned macro B

Both macros B and W_M don't exist.

The user is not able to see the macros because the module (where the
macros are) has Option Private Module
Macros are Subs responding to a click event.
General pattern is Button1 and Button1_Click


Any help, hint, pointer is appreciated

Thank you
N