Excel 2003 - "interesting" feature when running macros
 

I had developed some macros that ran fine in Excel 2002 and 2000.
Still, when I first got to run them on Excel 2003 I ran into something I
don't understand: when I pressed a button in the sheet, Excel opened (by
itself) the VB project and waited for me to press the "Run" button in order
to actually run that macro. After I pressed the "Run" button they ran fine,
just like in the older Excel versions.
The macro security is set to medium for the Excel 2003 I on which I ran that
time, so that I get the usual prompt to enable/disable macros for the
workbook I open.
Is there something I missed?
Cause this thing is quite annoying for users...

Excel 2003 - "interesting" feature when running macros
 

The "interesting" feature I ran into some days ago appeared no more yesterday
(being in the same place and on the same computer).
That's lucky.
Still, I can't figure what happened and wether it's gonna happen again and
when ...
Any suggestions?