rel="nofollow" disappeared after editing URL

I have Rel Attribute = "nofollow" setting.
After editing node (URL value) I've got rel="nofollow" disappeared.

I've take a look at database:
"field_link_attributes" value changed from "N;" to "a:3:{s:6:"target";s:7:"default";s:5:"class";s:0:"";s:3:"rel";s:0:"";}"