PSD would white out objects that I am busy working on

Example: I am busy with a shape and want to give the shape a drop shadown, as soon as I go into the drop shadown settings the element gets whited out (looks like a glitch).
It has been been doing this on random objects that I am n ot even working on. It literally just takes any thing. The only way I get the white block away is to zoom in or out or beter to hide and unhide an object.

Please let me know what is happening here?