The below example works fine under Ruby 1.8 with the same configuration.
In Ruby 1.9.1, there is no limiting happening, thus all matches are displayed.
{"type":"Update", "plus":["published_at",{}], "limit":1}
Hmm, very interesting. Thanks for letting us know -- we've only been testing under 1.8x so far.
ruby 1.9 is fully supported as of wagn 1.8
--Ethan McCutchen.....Sun Mar 25 03:55:43 +0000 2012