possible bug in new slur code

[Graham Percival]

How powerful is the new slur code supposed to be?  In the following 
file, the "2" is touching the slur.  Is the new slur code supposed to 
avoid such conditions (in which case this is a bug report), or is this 
just a far-off feature request?  :)

This is with fink lilypond-unstable 2.3.8

\score { \notes{
\clef alto
\time 3/4
cis''2(^1 a'4)^2
}}