[cairo] [rcairo] memory leaks by 'pop_group(false)'

[Binzo]

Hello,

I have met a memory leak problem with rcairo 1.5.0.

The calling Cairo::Context#pop_group(false) to generate surface
pattern as a object seems to leak memory.
Cairo::Context#push_group(nil, false) { ... } also showed same
problem.

Here is a test script for this problem.
---
require "cairo"

s = Cairo::ImageSurface.new (:argb32, 400,400)
c = Cairo::Context.new(s)

10000.times do |i|
puts i
c.push_group
c.pop_group(false)      ### memory leaks occured here
sleep  0.05
end
---

I use rcairo-1.5.0 installed by gems and the version of ruby is
ruby 1.8.6 (2007-12-19 patchlevel 5000) [i686-darwin8.11.1]

Is this a problem only on my environment ?