py4web: some error on DB

During convertion of web2py to py4web; I fall on some error in controller that return a none value for an existing entry in database.

In some case, same call of type db.sequence_file[id] return fisrt a correct value, and a second call one line under return none value.
Hard to reproduce, not constant, ...

@clement.chesnin sugfgest to use row.update(**values) and row.validate_and_update(**values). Don't know if it will be enough.