Hi,
On Mikalai Zaikin's page http://java.boot.by/scbcd5-guide/ch06.html is described EntityManager remove operation.
For entity in removed state is sentence : "If A is a REMOVED entity, it is IGNORED" .
Is it correct ? Seems that for such situation we get IllegalStateException.
According to the specification (and that's where the guide you're using took the information from), invoking remove on a removed entity will be ignored.
3.2.2 Removal
If X is a removed entity, it is ignored by the remove operation.