I just found out that this happens only in Firefox.
And if I reload pressing Ctrl+F5, it works. If I press just F5, or Ctrl+R, or hit the reload button, it doesn't work.
It works in IE in all the ways above.
so which RF version you using? if you using ajax4jsf oldest separate releases - you'll have to upgrade because it's not supported after merge as separate library.
Also provide please page code, bean sample and info about bean scope.