When I use a modifier, they work fine, but when I use the Mesh Deform Modifier it is not visible for some reason. When I move any other modifier, it becomes visible; if I let go of it, it turns back to being invisible.
Also the modifier underneath it become only togglable. Any other button I select ( The Drop Down menu with the options to move first or last, apply Modifier, etc...) aren't selectable.
I am also unable to duplicate the modifier
I have reinstalled Blender. and it has changed nothing.
Edit:
After a few hours away, I came back to find it still the same. However I did encounter the steps to generate the problem;
Make two Mesh Deform Modifiers and apply both to a mesh. I first have an armature modifier, a corrective smooth modifier, subsurf, and then the two Mesh Deforms last.
I tried to rearrange the stack of the mods since I remember reading somewhere that the order in which the Modifiers are stacked yields undesirable results, and wouldn't I know it, just by rearranging the stacks the second mesh deform disappeared from the UI, so adjusting the stack generates this issue.
However, rearranging them, does not solve this one for me.
I will get a photo uploaded soon to show what I mean.
The first photo on top you can see the extra space between the modifiers
In the first image above you can see the modifiers are visible, but only when I select the upper right corner to move/ rearrange the modifiers within the Stack.

