Qt Plugins - more than one of the same tyoe in one plugin directory

Hello,

let me try to explain my problem. I got an interface class and two classes derived from it that should be used as plugins. Good news: everything compiles and works fine if only one of the libMyClassA.so/libMyClassB.so is in the plugin directory (where i try to load plugins with QPluginLoader).
But: if i put the second plugin into the plugins directory (so now i got libMyClassA.so and libMyClassB.so) i get strange errors from QPluginLoader while loading.
Error on loading classA: undefined reference to classB::someFunction
Error on loading classB: undefined reference to classA::someOtherFunction

What's strange is that
a) these functions exist
b) why do i get an error when loading plugin with classA about something in classB (and vice versa) cause the plugin if the only on in the dir works!!! (even stranger: there are no includes or whatever that tell classA that classB exists!)

If someone could shed light one this i would be really glad.

Thx in advance,

Roland