Throw in Fiber causes loop

e$B$3$s$P$s$O!"e(Bsheepman e$B$G$9!#e(B

Fiber e$B$N%V%m%C%/$NCf$G%-%c%C%A$5$l$J$$e(B throw e$B$r8F$V$H!"e(B
e$BL58B%k!<%We(B e$B$K4Y$j$^$9!#e(B

$ cat f2.rb
Fiber.new do
throw :a
end.yield

$ ruby-1.9 -v f2.rb
ruby 1.9.0 (2007-06-04 patchlevel 0) [i686-linux]
(e$B0J2<L58B%k!<%We(B)