The problem was something about deployment, that the new compatible Lucene.dll was replaced by the incompatible Sitecore7 dll.
So, if both lucene.net and lucene.net.contrib dll are referenced, it should work.
Not directly the solution to my question, but this source is worth mentioning again. (About lucene.dll versions) : http://laubplusco.net/sitecore-7-lucen-3-0-highlighted-results/