What version and hotfix are you using and what is your CI setup - excluded, included objects? I just tested this on 13.0.130 and it is working fine. I see the change tracked in
\CMS\App_Data\CIRepository\@global\cms.formclass\bizform.dancinggoatcorecontactusnew.xml
(Screen shot link)
I am using the sample Dancing Goat project and the dancinggoatcorecontactusnew
is the code name of my online form. Are you able to reproducee it using out of the box installation as well? So we have the same code base.