Press equals. You're seeing the 23 you entered, not the sum. If you enter it very slowly, you'll see 3 until you press =.

Same, I am getting 23 too.

I think the problem is due to the UI is lagging and thus the second addition click event is not registered. e.g: 4+5+6 will return you 56.

Edit: Did it without using the "=" as other has pointed out.

Are you pressing ”=” to get the actual result?