New date format in gemspec breaks older rubygems version

I forget why but I'm stuck using rubygems 1.7.2, which means I
occasionally get the dreaded "invalid date format in specification"
error message

What sets the date format?

For example. with rubygems-bundler

Invalid gemspec in [/usr/local/rvm/rubies/ree-1.8.7-2011.03/lib/ruby/
gems/1.8/specifications/rubygems-bundler-0.2.6.gemspec]: invalid date
format in specification: "2011-09-16 00:00:00.000000000Z"

If you look on github the date is 2011-09-16. no time information is
added
https://github.com/mpapis/rubygems-bundler/blob/master/rubygems-bundler.gemspec

So what adds the 00:00:00.000000000Z? Is it part of the rubygems
push process?

This gem supports older versions of rubygems but once it is uploaded
to rubygems.org it will only work on 1.8.x :-\

Thanks for any pointers.
Tony

FYI.. The Gem author fixed this issue by rebuilding the Gem with
1.8.7. He mentioned something about the YAML version. I guess I
should learn about the Gem deploy process to better understand what
the root cause of the issue was.

The fix
https://github.com/mpapis/rubygems-bundler/commit/ead8ec8d57331b6b750d1622e5b683763b92fd73#diff-1

The ticket
https://github.com/mpapis/rubygems-bundler/issues/6