I noticed, that you can actually press a Hotkey in the "Add new mod element" window, like the letter T for a new Tool mod element, or G for a new GUI element, etc.
And after pressing one Hotkey, your desired mod element get's selected.
But for some odd reason, the mod element actually stays as a "new Block element", as you press next after you typed a name in.
Here is a Tutorial with Pictures to recreate this Bug:
First, press the + to open the "New mod element" window:
Second, press a Hotkey (I pressed T for Tool) but it is still a block type:
Third, type a name in, and press OK:
Fourth, as you can see, it brings up the block editor!