When you have a gate in your hand the game perfomance is good, however when you look at any block with a gate in your hand you get a preview, which gives a big frame drop:

They also look a bit funny in all F5 modes.

No longer an issue with newer versions see Work in progress / Project for further details.

As you can see, without a gate preview the game is at 30 FPS, but with preview it falls into 8 FPS.
And with the analogic gate (Comparator) the same happens.
(It happens with all the gates :P).

I would expect that, yeah, as it renders the gate again every render tick. This is not a bug but I will add a way to cache the rendering so it doesn't need to be re-rendered every time :P