JDOUserException when persisting object: supposedly incorrect type is same as expected type - jdo

Question

Trying to persist an object results in this exception being thrown. It complains about an incorrect type but then expects that same type. The exception started appearing after renaming the project from dbd2012_p2 to dbd2012_p3 (it's a continuation from the previous assignment).
I have found no information on Google about this exception. I've gone through the metadata files making sure there are no instances of dbd2012_p2 left behind and I am now stumped.
Our database is basically a many-to-many relationship: Prova with Tag. Mesura models the relationship with a few extra attributes (activity, datetime, x, y and z coords).
Exception
javax.jdo.JDOUserException: The owner field prova of element class dbd2012_p3.Mesura has an incorrect type "dbd2012_p3.Prova". Should be "dbd2012_p3.Prova"
javax.jdo.JDOUserException: The owner field prova of element class dbd2012_p3.Mesura has an incorrect type "dbd2012_p3.Prova". Should be "dbd2012_p3.Prova"
at org.datanucleus.api.jdo.NucleusJDOHelper.getJDOExceptionForNucleusException(NucleusJDOHelper.java:519)
at org.datanucleus.api.jdo.JDOPersistenceManager.jdoMakePersistent(JDOPersistenceManager.java:736)
at org.datanucleus.api.jdo.JDOPersistenceManager.makePersistent(JDOPersistenceManager.java:756)
...
at dbd2012_p3.dbd2012_p3.main(dbd2012_p3.java:28)
Code
for (String name : names) {
for (String seq : seqs) {
Prova prova = new Prova(name, seq);
pm.makePersistent(prova); // Exception thrown here
}
}
Prova.java
#PersistenceCapable
public class Prova {
#PrimaryKey //OJO
private String nom_persona = null;
#PrimaryKey
private String num_seq = null;
private Set tagRelations = new HashSet();
public Prova(String nou_nom_persona, String nou_num_seq) {
nom_persona = nou_nom_persona;
num_seq = nou_num_seq;
}
public Prova(){}
package-mysql.orm
This is how we have our tables defined:
<?xml version="1.0"?>
<!DOCTYPE orm SYSTEM "file:/javax/jdo/orm.dtd">
<orm>
<package name="dbd2012_p3">
<class name="Prova" type="application" table="prova">
<field name="nom_persona" primary-key="true">
<column name="nom_persona" length="45" jdbc-type="VARCHAR"/>
</field>
<field name="num_seq" primary-key="true">
<column name="num_seq" length="45" jdbc-type="VARCHAR"/>
</field>
<field name="tagRelations" persistence-modifier="persistent" mapped-by="prova">
<collection element-type="Mesura" />
</field>
</class>
<class name="Tag" type="application" table="tag">
<field name="codi" primary-key="true">
<column name="codi" length="45" jdbc-type="VARCHAR" />
</field>
<field name="nom">
<column name="nom" length="45" jdbc-type="VARCHAR" />
</field>
<field name="provaRelations" persistence-modifier="persistent" mapped-by="tag">
<collection element-type="Mesura" />
</field>
</class>
<class name="Mesura" type="datastore" table="mesura">
<field name="datetime" column="datetime"/>
<field name="prova" />
<field name="tag" />
<field name="activitat" />
<field name="x">
<column name="x" jdbc-type="DECIMAL" length="3" scale="1" />
</field>
<field name="y">
<column name="y" jdbc-type="DECIMAL" length="3" scale="1" />
</field>
<field name="z">
<column name="z" jdbc-type="DECIMAL" length="3" scale="1" />
</field>
</class>
</package>
</orm>
Note: I haven't tagged this as homework because the assignment is about applying data mining techniques to the data we add into the database. I can just rename the project back to its old name and it works again, but the exception is really bugging me.