convert-ly and verticalExtent

[Daniel Johnson]

I have begun migrating my 2.6 files to 2.8 syntax.  In 2.6, I have used 
the following combination to force vertical-extent of a Staff in a 
ChoirStaff so lyrics can be centered between staves:

\set Staff.minimumVerticalExtent = ##f
\set Staff.verticalExtent = #'(-3.25 . 3.25)

When I run this through convert-ly, it converts the first line to:
   \override Staff.VerticalAxisGroup #'minimum-Y-extent = ##f
However, it does NOT convert the second line at all.  For correct 
behaviour, the second line should be converted to the following:
   \override Staff.VerticalAxisGroup #'Y-extent = #'(-3.25 . 3.25)

Was this a conscious decision, or simply an oversight?

Regards,
--Daniel