I've found what's the problem, I'm posting the solution for those who have the same problem.
I've checked all the possibilities, from a compilation from source to an update of gtk2 and wxwidgets from ustable, but there were no change. So I checked the last Amule's dependence, libcrypto++. The version used for Amule in testing is 5.5, and 5.2 in stable. So I uninstalled libcrypto++ 5.5 and installed the 5.2 version and Etch version of Amule, and it works perfectly.
So, sorry guys, it wasn't an Amule bug after all.