When RESTful API is used with 5.3.0 ER4 and you use it to create package "A/B" (package "B" is a child of "A"), what is actually created is "A/_B" (package "_B" is a child of "A").

The problem lies here:
https://github.com/droolsjbpm/guvnor/blob/5.3.x/guvnor-webapp/src/main/java/org/drools/guvnor/server/jaxrs/CategoryResource.java#L153

Instead of properly understanding the "/" as a separator of two category names, the code just puts the "/" at the beginning on the child category's name. And this name is later replaced with "_".

The fix is fairly trivial:
name = categoryPath.substring(lastDotIndex + 1);