There is what's called a bi-metal strip that releases these covers. The first thing I would do is lift out the the wash arm and check if the filter under the wash arm is clogged. It is the motor load that creates the current load that heats up the bi-metal strip that releases the little clips that release the covers. If the filter is clogged, the water flow is not strong enough to put enough of a load on the motor to heat the bi-metal to open the covers.
It could be the that the dispenser needs replacing, but check the filter first.