\once broken?

[Juergen Reuter]

Hi!

2.1.22 breaks quite a *lot* of ancient implementation, e.g.
refman section 3.15.8, \virgula and \caesura command;
section 3.15.9.2, many of the ligatures in the neumes table;
section 3.15.11, Sanctus example, etc.

What seems to be common among all these examples is that a property that 
should affect only a single item actually affects all following items.  
For example, in refman section 3.15.8, \finalis issues

\once \override BreathingSign  #'print-function = #Breathing_sign::finalis

(cp. ly/gregorian-init.ly), which should have an effect only once, but it 
looks as if print-function is still set to finalis when \virgula and 
\caesura are performed afterwards, such that they have no effect.  Is this 
a bug or an intended change in the semantics of \once?

Greetings,
Juergen