Ruby 1.8.x + I18N String Interpolation with % and %% and <

Upgrading from Rails 2.3.5 to Rails 2.3.8 exposed the following problem with the String#% method where interpolation is performed.

'%.0f<span>%%</span>' % 0.5

Expected result is "0<span>%</span> but instead there is an exception thrown:

malformed format string - %<

This is from the file:

activesupport/lib/active_support/vendor/i18n-0.3.7/i18n/core_ext/string/interpolate.rb

Where the line in question is:

result = gsub(/%([{<])/, '%%\1')

This is presumably trying to re-escape the angle-bracket style placeholders so they aren't evaluated. The problem is that this is ignoring already escaped % characters.

A possible fix for this is to make it not try and re-escape:

result = gsub(/%%?([{<])/, '%%\1')