Do not set value of keys in modified fields

issue3225
review910002
(transplanted from a65b1e9e783d736c03b6162b5a2bc3d4a47640d0)

--HG--
extra : transplant_source : %A6%5B%1E%9Ex%3Dsl%03%B6%16%2BZ%2B%C3%D4%A4v%40%D0