ZODB undo problems

[erik_w]

I thought transactions in ZODB was 'undoable'.  Still calling
db.undo() seems not to work (see below).  What have I missed?

PythonWin 2.1.1 (#20, Jul 20 2001, ...
Portions Copyright 1994-2001 Mark ....
>>> from ZODB import FileStorage, DB
>>> storage = FileStorage.FileStorage('slettes.zdb')
>>> db = DB(storage)
>>> conn = db.open()
>>> root = conn.root()
>>> db.supportsUndo()
1
>>> root['r1'] = 0
>>> for i in range(10):
... 	root['r1'] += 1
... 	get_transaction().commit()
... 	
>>> root['r1']
10
>>> undoID = db.undoLog(0,100)[0]['id']
>>> db.undo(undoID)
>>> root['r1']
10
>>>get_transaction().commit()  #do I need this?
>>> root['r1']
10
>>> #huh...

AMK's standalone ZODB, most recent version.

Anyone out there with good pointers to pages on ZODB programming? 
(in addition to those on amk.ca and zope.org).

    BR
    EW