In the small circuit as seen in the screenshot, the following is what I expect to happen:

Minecarts go in top Hopper. When a minecart is inserted into dispenser, the comparator powers a block in front of itselfs, which powers the redstone dust, which powers the block above the comparator, adjacent to the bottom hopper, which stops the hopper from accepting/delivering more minecarts.
When the dispenser is powered it dispenses a minecart, turning off the comparator, depowering the hopper, which allows a new minecart to be placed in the dispenser.
The dispenser itself is powered by a block, powered by a redstone torch (normally OFF).

What does happen is:
I push the button and one minecart is dispensed. Push it again and nothing happens.

HOWEVER, when the redstone dust is removed, few seconds later the dispenser starts working again when the button is pushed.

Set up this circuit and test for yourself.