Phrasing Slurs only from another slur start?

[Nils]

Hello list,

Is it intended or a bug that you have to start a phrasing slur and a normal 
slur only at the same time? This means you can only have one normal slur in a 
phrasing slur (from the beginning?)

The example 
http://lilypond.org/doc/v2.11/Documentation/user/lilypond-learning/Ties-and-slurs
 
shows nested slurs, called phrasing slurs with a special syntax: 

a8(\( ais b c) cis2 b'2 a4 cis,\)

You need these type of slurs if you have (several) melisma(s) but want 
phrasing/legato also.

However my Lilypond install 2.13.58 complains if I start the phrasing slur (\ 
anywhere else except right before the normal slur, as seen in the example.

Is this a bug?

Nils