Hi Edson, and thanks for answering

? - are the fact types (classes) in the same package or different packages?
Different packages. But I tried this on my little sample (put the sub-class in another package than the mother class), and this works

? - Are the declaration(s)/rules in the same file or different files?
Same file (DRL)

? - Are you using a single kbuilder to build the whole thing on your application or using different kbuilders?
? - Is the order in which you are loading the files into the kbuilder and the order you add packages in your kbase the same on your application and your test?
My kbase has a unique package, got from a single DRL file, built by a single (new) kbuilder.

But I use one kbuilder per package, only for build time, and I have other packages / kbases, for other rule sessions ...
Here I create 3 packages (and 3 kbases), using one new kbuilder for each. These 3 packages don't have any fusion construction in them.
Then I build the 4th package / kbase, using one new kbuilder, and this is this package which contains some fusion rules.
Does kbuilders can collide in some way ? May be that as the 3 first package don't use any fusion, all the classes are tagged as "not event", kept somewhere, and reused in the 4th kbuilder, that only update the explicitely "event" classes ? I will try to load the fusion kb first to see what happend ... but I am sceptic, as the 3 first package don't use the ***Event objects ...

There is another difference on my package build process.
My little test is built over the Hello World sample. My app uses more sophisticated way of getting resources, but finally calls the same kbuilder.add... magic method ...
The only difference is that :
    - HelloWorld sample, and my little test, uses  kbuilder.add( newClassPathResource(...) , ResourceType.DRL) to get resources that are located in a eclipse source folder
    - My application uses kbuilder.add( newFileResource(...) , ResourceType.DRL) to fetch resources in the file system