Hello Sophie,
I am not sure which CMS you use, but I personally have not used the keywords meta tag for some time now. Not due to it being a spam signal, but simply because it is no longer used as a ranking factor.
To alleviate your issue and not show your tag but still continue to use the CMS field, could your developers not look into the template files that are used and remove the location where a meta tag is dynamically added to your header. That way the CMS can still have the field for search queries but not be present in the pages code structure.
That way you get the best of both worlds, without causing you any issues. Hopefully I have understood how your site works and this is a possible solution.
Tim
