Looks like you are still using the “classic” IPTC stationary pad. In the normal stationary pad, there is no “+” checkmark for the caption, but a button that switches between prefix, replace, and append (it will also be on the left, not on the top).
As the classic version is deprecated (and probably no longer really supported), I suggest you switch to the new one (which can be heavily customised to match what you now have).
