Starting in jruby-1.7.5 the compareTo of Dates converted to java objects seems to be broken:

in 1.7.4:
jruby-1.7.4 :003 > Date.today.to_java.compareTo((Date.today - 1).to_java)
=> 1
jruby-1.7.4 :004 > Date.today.to_java.compareTo((Date.today).to_java)
=> 0
jruby-1.7.4 :005 > Date.today.to_java.compareTo((Date.today + 1).to_java)
=> -1

In 1.7.5:
jruby-1.7.5 :005 > Date.today.to_java.compareTo((Date.today - 1).to_java)
=> 0
jruby-1.7.5 :006 > Date.today.to_java.compareTo((Date.today).to_java)
=> 0
jruby-1.7.5 :007 > Date.today.to_java.compareTo((Date.today + 1).to_java)
=> 0

This is also the case in the 1.7.10 release.