I had the same problem of not being able to get the ovals into the square holes of the operators. I’m on a Mac using Chrome.
The bug is that if your mouse is in the middle of a long oval when you drag it, the “target” box won’t “light up” to accept the drag-and-drop.
However, if you put the mouse cursor most of the way to the left of a long oval, then when the mouse cursor is over the target box, it WILL light up and allow the drag and drop.
The actual “logic” is that the left-hand side of the oval is what has to be over the target. When your mouse cursor is in the middle, you put the mouse over the box and it doesn’t drop. With the mouse cursor at the left, it corresponds with the “hot spot” of the oval, and it seems to work.
In actuality, it doesn’t matter where your mouse cursor is; you just need to drop the far-left side of the oval onto the target box of the operator.