Voices appearance

Hi all,

Ich have entered a staff with 4 different voices and everything work out so far. However when I try to display the single voices the first one ( in my case a Tenor Sax) does not show the single voice but the full staff with all 4 voices while the others are displayed as single voices as it should be.
Even when I try to export the single voices into an pdf file I have the same problem: the Tenor Sax voice is exported as fullstaff while the others appear as single voice pdf.
Any idea how to fix this.

Thx Kai