linestring buffer with rgeo and geos

[tagliala]

For a project I'm working on, I needed a buffer around a linestring. I'm using rgeo 0.3.20 + geos 3.4.2 on osx 10.9

this is a snippet of my ruby code:

factory = RGeo::Geographic.simple_mercator_factory(buffer_resolution: 2)
line_string = factory.line_string(points)
line_string_buffer = line_string.buffer(3000)

Most of the times, the result of the above is a POLYGON, other few times is an "odd" MULTIPOLYGON:

Examples: http://jsfiddle.net/tagliala/2qu9f/ and http://jsfiddle.net/tagliala/LhSx6/

(The only difference is a point added to the linestring. You could zoom in to see that)

Is there a way to always obtain a polygon?

I tried to increase the buffer resolution to 8 and it fixes the problem for this specific case, but I'm afraid it isn't a proper solution. Moreover, my application doesn't need so much precision.

Thanks In Advance

PS: to be honest, I also asked on the rgeo-users group and stackoverflow but there seems to be very low visibility, 9 total views (including me) in 7 days.