The script allow to reproduce a traceback on xapian 1.4.5 (with python2)
To run the test just do:

   $ python2 test.py

The test run some xapian operations N times on Chert/Glass backends.
(we run it N times because the error don't occur every time?)
The script create many documents with many stored values and try to display this stored values.
There's only problem with Glass backend when trying to display the stored values:
The error is:

    > document.get_value(0)
    > xapian.DatabaseCorruptError: Db block overwritten - are there multiple writers?

Sometimes, the database is corrupted after this error:

    > catalog.replace_document(term, xdoc)
    DatabaseCorruptError: Expected block 200713 to be level 2, not 1

Example of result:

	Test 1/5 glass
	Traceback (most recent call last):
	  File "./test_xapian.py", line 71, in <module>
		t.test(backend)
	  File "./test_xapian.py", line 46, in test
		value1 = document.get_value(0)
	xapian.DatabaseCorruptError: Db block overwritten - are there multiple writers?
	> Error
	Test 1/5 chert
	> Success
	Test 2/5 glass
	Traceback (most recent call last):
	  File "./test_xapian.py", line 71, in <module>
		t.test(backend)
	  File "./test_xapian.py", line 46, in test
		value1 = document.get_value(0)
	xapian.DatabaseCorruptError: Db block overwritten - are there multiple writers?
	> Error
	Test 2/5 chert

	> Success
	Test 3/5 glass
	Traceback (most recent call last):
	  File "./test_xapian.py", line 71, in <module>
		t.test(backend)
	  File "./test_xapian.py", line 46, in test
		value1 = document.get_value(0)
	xapian.DatabaseCorruptError: Db block overwritten - are there multiple writers?
	> Error
	Test 3/5 chert
	> Success
	Test 4/5 glass
	Traceback (most recent call last):
	  File "./test_xapian.py", line 71, in <module>
		t.test(backend)
	  File "./test_xapian.py", line 46, in test
		value1 = document.get_value(0)
	xapian.DatabaseCorruptError: Db block overwritten - are there multiple writers?
	> Error
	Test 4/5 chert
	> Success
	Test 5/5 glass
	Traceback (most recent call last):
	  File "./test_xapian.py", line 71, in <module>
		t.test(backend)
	  File "./test_xapian.py", line 46, in test
		value1 = document.get_value(0)
	xapian.DatabaseCorruptError: Db block overwritten - are there multiple writers?
	> Error
	Test 5/5 chert
	> Success
	========================================
	========================================
	{'chert': {'errors': 0, 'success': 5}, 'glass': {'errors': 5, 'success': 0}}
	========================================
	========================================