Concurrency issue with JSword - bd1.getSAXEventProvider(); throws "Root Element not set"

Caused by: java.lang.IllegalStateException: Root element not set
at org.jdom.Document.getRootElement(Document.java:218)
at org.crosswire.jsword.book.filter.osis.OSISFilter.parse(OSISFilter.java:149)
at org.crosswire.jsword.book.filter.osis.OSISFilter.toOSIS(OSISFilter.java:74)
at org.crosswire.jsword.book.basic.AbstractPassageBook.getOsisIterator(AbstractPassageBook.java:90)
at org.crosswire.jsword.book.BookData.getOsisContent(BookData.java:157)
at org.crosswire.jsword.book.BookData.getOsisFragment(BookData.java:100)
at org.crosswire.jsword.book.BookData.getSAXEventProvider(BookData.java:113)
at com.tyndalehouse.step.core.service.impl.JSwordServiceImpl.getOsisText(JSwordServiceImpl.java:131)
at com.tyndalehouse.step.core.service.impl.BibleInformationServiceImpl.getPassageText(BibleInformationServiceImpl.java:57)
at com.tyndalehouse.step.rest.controllers.BibleController.getBibleText(BibleController.java:101)
at com.tyndalehouse.step.rest.controllers.BibleController.getBibleText(BibleController.java:60)
... 28 more

@Test
public void testConcurrencyIssueOnBookData() throws NoSuchKeyException, BookException,
InterruptedException {
final String[] names =

{ "KJV", "ESV" }

;
final String ref = "Rom.1.1";

final Runnable r1 = new Runnable() {
@Override
public void run() {
final Book b0 = Books.installed().getBook(names[0]);
BookData bd1;
try

{ bd1 = new BookData(b0, b0.getKey(ref)); bd1.getSAXEventProvider(); } catch (final NoSuchKeyException e) { e.printStackTrace(); } catch (final BookException e) { e.printStackTrace(); }

}
};

final Runnable r2 = new Runnable() {
@Override
public void run() {
final Book b0 = Books.installed().getBook(names[1]);
BookData bd1;
try { bd1 = new BookData(b0, b0.getKey(ref)); bd1.getSAXEventProvider(); }

catch (final NoSuchKeyException e)

{ e.printStackTrace(); } catch (final BookException e) { e.printStackTrace(); }

}
};

int ii = 0;
while (ii++ < 1000)

{ final Thread t1 = new Thread(r1); final Thread t2 = new Thread(r2); t1.start(); t2.start(); t1.join(); t2.join(); }

}