[pysqlite] [apsw] ReadOnlyError when closing read-only blobs?

I've found that Blob.close() throws a ReadOnlyError if I've previously
attempted to perform a write on that blob. I was surprised by this,
but I wanted to see if this is expected behavior.

Here's code that demonstrates the issue:

  import apsw

  sql = '''
  CREATE TABLE IF NOT EXISTS data
  (id INTEGER PRIMARY KEY NOT NULL,
   data BLOB NOT NULL)'''

  conn = apsw.Connection('test.db')
  cur = conn.cursor()
  cur.execute(sql)
  cur.execute('INSERT INTO data VALUES(?,?)', (None, apsw.zeroblob(1000)))
  rowid = conn.last_insert_rowid()
  blob = conn.blobopen('main', 'data', 'data', rowid, False)

  # Attempt a write
  try:
    blob.write('x' * 10)
  except apsw.ReadOnlyError:
    # expected
    pass

  # This throws ReadOnlyError unexpectedly
  blob.close()

This is with version 3.6.16 on python 2.6.1.

Austin