What has happened to "this x" option for plugins?

I’m not sure if this problem is specific to plugins but I have noticed in a plugin I built and the toolbox plugin
Toolbox plugin:
image
Plugin I built:
image

I can copy the expression from an action that was built a week or two ago (presumably before any change that caused this bug) and the expression evaluates correctly. Here is a screenshot of the exact same place as above just with the expression pasted in:
image

I can still get the value I want by referring to the element itself:
image

But the the “This X” was always at the top and just made things so easy. What happened bubble?