jekyll sort date issue

gistfile1.txt

[458 pstam-blog]$ /Users/stammy/code/jekyll/bin/jekyll build --watch --trace
Configuration file: /Users/stammy/code/pstam-blog/_config.yml
            Source: .
       Destination: ./_site
      Generating...
  Liquid Exception: comparison of Jekyll::Document with Jekyll::Document failed in photos/index.html
/Users/stammy/code/jekyll/lib/jekyll/filters.rb:215:in `sort': comparison of Jekyll::Document with Jekyll::Document failed (ArgumentError)
	from /Users/stammy/code/jekyll/lib/jekyll/filters.rb:215:in `sort'
	from /Users/stammy/.rbenv/versions/1.9.3-p448/lib/ruby/gems/1.9.1/gems/liquid-2.5.5/lib/liquid/strainer.rb:43:in `invoke'
	from /Users/stammy/.rbenv/versions/1.9.3-p448/lib/ruby/gems/1.9.1/gems/liquid-2.5.5/lib/liquid/context.rb:75:in `invoke'
	from /Users/stammy/.rbenv/versions/1.9.3-p448/lib/ruby/gems/1.9.1/gems/liquid-2.5.5/lib/liquid/variable.rb:50:in `block in render'
	from /Users/stammy/.rbenv/versions/1.9.3-p448/lib/ruby/gems/1.9.1/gems/liquid-2.5.5/lib/liquid/variable.rb:38:in `each'
	from /Users/stammy/.rbenv/versions/1.9.3-p448/lib/ruby/gems/1.9.1/gems/liquid-2.5.5/lib/liquid/variable.rb:38:in `inject'
	from /Users/stammy/.rbenv/versions/1.9.3-p448/lib/ruby/gems/1.9.1/gems/liquid-2.5.5/lib/liquid/variable.rb:38:in `render'
	from /Users/stammy/.rbenv/versions/1.9.3-p448/lib/ruby/gems/1.9.1/gems/liquid-2.5.5/lib/liquid/tags/assign.rb:26:in `render'
	from /Users/stammy/.rbenv/versions/1.9.3-p448/lib/ruby/gems/1.9.1/gems/liquid-2.5.5/lib/liquid/block.rb:106:in `block in render_all'
	from /Users/stammy/.rbenv/versions/1.9.3-p448/lib/ruby/gems/1.9.1/gems/liquid-2.5.5/lib/liquid/block.rb:93:in `each'
	from /Users/stammy/.rbenv/versions/1.9.3-p448/lib/ruby/gems/1.9.1/gems/liquid-2.5.5/lib/liquid/block.rb:93:in `render_all'
	from /Users/stammy/.rbenv/versions/1.9.3-p448/lib/ruby/gems/1.9.1/gems/liquid-2.5.5/lib/liquid/block.rb:82:in `render'
	from /Users/stammy/.rbenv/versions/1.9.3-p448/lib/ruby/gems/1.9.1/gems/liquid-2.5.5/lib/liquid/template.rb:124:in `render'
	from /Users/stammy/.rbenv/versions/1.9.3-p448/lib/ruby/gems/1.9.1/gems/liquid-2.5.5/lib/liquid/template.rb:132:in `render!'
	from /Users/stammy/code/jekyll/lib/jekyll/convertible.rb:96:in `render_liquid'
	from /Users/stammy/code/jekyll/lib/jekyll/convertible.rb:199:in `do_layout'
	from /Users/stammy/code/jekyll/lib/jekyll/page.rb:122:in `render'
	from /Users/stammy/code/jekyll/lib/jekyll/site.rb:261:in `block in render'
	from /Users/stammy/code/jekyll/lib/jekyll/site.rb:260:in `each'
	from /Users/stammy/code/jekyll/lib/jekyll/site.rb:260:in `render'
	from /Users/stammy/code/jekyll/lib/jekyll/site.rb:43:in `process'
	from /Users/stammy/code/jekyll/lib/jekyll/command.rb:53:in `process_site'
	from /Users/stammy/code/jekyll/lib/jekyll/commands/build.rb:46:in `build'
	from /Users/stammy/code/jekyll/lib/jekyll/commands/build.rb:30:in `process'
	from /Users/stammy/code/jekyll/lib/jekyll/commands/build.rb:17:in `block (2 levels) in init_with_program'
	from /Users/stammy/.rbenv/versions/1.9.3-p448/lib/ruby/gems/1.9.1/gems/mercenary-0.3.3/lib/mercenary/command.rb:220:in `call'
	from /Users/stammy/.rbenv/versions/1.9.3-p448/lib/ruby/gems/1.9.1/gems/mercenary-0.3.3/lib/mercenary/command.rb:220:in `block in execute'
	from /Users/stammy/.rbenv/versions/1.9.3-p448/lib/ruby/gems/1.9.1/gems/mercenary-0.3.3/lib/mercenary/command.rb:220:in `each'
	from /Users/stammy/.rbenv/versions/1.9.3-p448/lib/ruby/gems/1.9.1/gems/mercenary-0.3.3/lib/mercenary/command.rb:220:in `execute'
	from /Users/stammy/.rbenv/versions/1.9.3-p448/lib/ruby/gems/1.9.1/gems/mercenary-0.3.3/lib/mercenary/program.rb:35:in `go'
	from /Users/stammy/.rbenv/versions/1.9.3-p448/lib/ruby/gems/1.9.1/gems/mercenary-0.3.3/lib/mercenary.rb:22:in `program'
	from /Users/stammy/code/jekyll/bin/jekyll:18:in `<main>'