Bug in "transform"?

The underlying issue is actually not in transform() but in data.frame():

aq <- airquality[sample(1:153,6),]
data.frame(aq, list(a=1,b=2))

Error in data.frame(aq, list(a = 1, b = 2)) :
 arguments imply differing number of rows: 6, 1

data.frame(aq, list(a=1))

   Ozone Solar.R Wind Temp Month Day a
3      12     149 12.6   74     5   3 1
31     37     279  7.4   76     5  31 1
34     NA     242 16.1   67     6   3 1
65     NA     101 10.9   84     7   4 1
59     NA      98 11.5   80     6  28 1
133    24     259  9.7   73     9  10 1