Forgot to mention that the server is correctly configured and that another example like this one, only packed in a jar instead of a ear is working without problems.
Further digging into the issue, I found this in my application deployment:
INFO [SettingsFactory] JDBC batch size: 15
INFO [SettingsFactory] JDBC batch updates for versioned data: disabled
...but I still haven't found how to enable it, or how to configure my app to stop using batch update.
This is too many replys by a single person on a thread, but I found the flag to enable the batch updates for versioned data, but it didn't help.
I'm guessing that the error is in that ORA-00928 and "select statement missing" message.
I am getting a little bit desprite, so help the dumb newbie if you can...
By accident, I finally found out what caused the error -
Incorrect mapping of class field/method to a column (in my later case it was filed "comment" on the column "comments"). It has nothing to do with batch support and alike.
tnx to everyone who tried to help out a noob ;)