Plague Nova bug?

I unchecked the checkbox for Plague Nova's weapon set.
Plague Nova disappeared from the skill bar and cannot be recovered.
Is this a bug?

Same happened to me, if you uncheck both weapon set ticks it bricks the gem:

Usually there are 2 tabs in the details - one for plague bearer and one for plague nova. They both disappear!

Even worse, the nova disappears from the shortcut skill assignment popup and you cannot use it anyway.

Frustratingly the animation for accumulating poison and even the top icon with percentage accumulated are still present.