I can't clarify further, since i have never seen the problem on any site, and there is no way to reproduce the problem without more information. My explanation was based on the source code of lang::util::translator_mode_p  and ad_get_client_property . Since "-cache-only" was not set in the call, and - as you said - you are not using a secure connection, the only option is that the empty value was coming from the database. ... but i have no idea, how it got there. Maybe related to your modifications?