Using String.matches() as a Query filter in JDO Query yields no results

Question

Using the code below:

Query query = newJdoQuery();
query.setFilter("identifier.matches('partner|account')");
query.execute();

yields no result. Why?

However, replacing the regex part with 'partner'. The query yields 1 result. Replacing it with 'account' yields another 6 results. Have a look at the image below.