possible bug with compound index.

I am using PostgreSQL 7.4.7
I have a table with serveral fields two of these are a serialno
(bigserial) and name(varchar).  I have created two indexs on these
fields.
    1) on name
    2) on name,serialno
if I use the command
'select * from table order by name limit 1'
everything is OK
if I use the command
'select * from table order by name desc limit 1'
everything is OK
if I use the command
'select * from table order by name,serialno limit 1'
everything is OK
if I use the command
'select * from table order by name,serialno desc limit 1'
The command is SLOW and gives back the INCORRECT data.
Doing an 'explain' on the above query says that the index wasn't used.