(see image) 

Here I have two droppers facing eachother. The dropper closest to the button has a bed inside. The other is empty. 

When the button is pushed, the dropper A places the bed in dropper B. Activating the comparator, and the two repeaters, which are on slowest setting, eventually signalling dropper B to put the bed back into A.

Everything appears to be in the state it was in origionally. 

However pressing the button again does nothing. It does not appear to activate the first dropper at all. 

Pressing the button the next time makes it work properly. 

This machine works only every other time the button is pressed. I do not understand why.