merge bug fix in R 2.15.0

Is it intended that the first suffix can no longer be blank? Seems to be
caused by a bug fix to merge in R 2.15.0.

$Rdevel --vanilla
DF1 = data.frame(a=1:3,b=4:6)
DF2 = data.frame(a=1:3,b=7:9)
merge(DF1,DF2,by="a",suffixes=c("",".1"))
Error in merge.data.frame(DF1, DF2, by = "a", suffixes = c("", ".1")) :
  there is already a column named ?b?

$R --vanilla
R version 2.14.2 (2012-02-29)

DF1 = data.frame(a=1:3,b=4:6)
DF2 = data.frame(a=1:3,b=7:9)
merge(DF1,DF2,by="a",suffixes=c("",".1"))

a b b.1
1 1 4   7
2 2 5   8
3 3 6   9

Matthew