OJS: Translator plugin - can't delete Extra Keys from locale

Hi, I’m working on Serbian Cyrillic translation and just have realised that I can’t delete extra keys from it, managing any other localization doesn’t give a problem, just this one, I have check file permissions and they are 755 on folders and 644 on files, just as on any other language file.

This sound very similar to the experience described here: Edit current unfinished translations - #38 by ctgraham