to_char() and order-by

Perhaps this was covered in the 7.2.x release notes, but it's mystifying us:

select to_char(time_link,'999.99') from stat_fetch
where time_link is not null
order by 1 desc limit 10;

(time_link is a double-precision column.) Under 7.1.3, this returns results like:

to_char
---------
9.99
9.99
9.99
9.99
9.99
9.99
9.99
9.99
9.99
9.99
(10 rows)

while under 7.2.1, you get the top 10 rows in *numerical* order:

to_char
---------
278.78
261.07
240.25
180.24
173.26
160.35
159.02
144.57
134.21
131.66
(10 rows)