I just upgraded to 1.91.4 (probably should have waited). I don't know if this is related to 1.91.4 but I don't recall having this problem with 1.90.x
Anyway, I have a table with a boolean field. In the model definition (db.define.....), it is set with default=False and writable=False. With these, it seems that web2py will set it as neither True nor False (None???). This doesn't seem to be a problem when I have writable=True (it will be set correctly to be False, as specified). Btw, I'm using sqlite.

