[web2py] contains return no rows of field list:string

[Joseph Jude]

I have the below table definition

db.define_table('entries',
Field('tags', 'list:string',required=True))

and then inserted values. Now I am trying to select using the below

entries = db(db.entries.tags.contains('learning')).select()

It returns no values (though there are rows in db).

db: sqlite; web2py: 1.99.4

Thank you,
Joseph