Problem with assertXPath and doubles

Hi all,

I'm writing you this email because I came across a problem when trying to
use assetXPath to check a double value.
I created this test https://gerrit.libreoffice.org/#/c/22196/ to cover the
opacity attribute, which is 0.5, however, If I do

assertXPath(pDocument, "/primitive2D/transform/mask/unifiedtransparence",
"transparence", "0.5");

it fails because the value it returns is 0 and the decimals are lost on
they way.

I've tried to debug it but I see that at this point:
http://opengrok.libreoffice.org/xref/core/test/source/xmltesttools.cxx#74,
it's already returning 0 so I don't know where else to see.

My question is: is this behavior intentioned? if not, could anybody give a
hint where the problem could be?

Best Regards,
Xisco