RapidMiner algorithms: numerical label not supported

[mirco-nasuti]

woken version: 9750bdc
woken-validation version: 9750bdc
knn version: 0.2.1 or naive-bayes version: 0.2.0

When using nominal variables with "integers" as categories (e.g. apoe4), RapidMiner complains (see woken logs) that : "numerical label not supported"