Xapian 1.4.5 "Db block overwritten - are there multiple writers?" with Glass

[Sylvain Taverne]

Hello,
Since the migration to xapian 1.4.X and the migration to Glass, i've
recurrent database corruption errors. I've to reindex my database to make
it works again.

    > DatabaseCorruptError: Expected block 200713 to be level 2, not 1

Theses problems always occur after this error:

    > xapian.DatabaseCorruptError: Db block overwritten - are there
multiple writers?

I've remarked the error occur when i'm trying to get stored values from a
database with a lot of stored values. I can reproduce the error with simple
python2 script i've posted on github

    https://github.com/staverne/xapian_test
    https://github.com/staverne/xapian_test/blob/master/test_xapian.py

The script always works with Chert backend but sometimes fail with Glass
backend.
It look's like the error report here:

    https://lists.xapian.org/pipermail/xapian-discuss/2017-May/009525.html

Any ideas ?
Cheers,
Sylvain