This an eight year old video, i know, but this pretty much explains the problem.
Anytime anything is converted to a symbol (mc, button, graphic) it disappears form the stage. This makes it very difficult for me to design because i can't see it.
I haven't seen any answer to this anywhere, but i hope someone has the answer.
(sry for my bad english and stuff)
That problem usually occurs if you have the layer set to "Show layer as Outline". Look at the layer where you are working, next to the layer name are three icons. The one on the right that looks like a box is the Outline control. This control will toggle the object in the layer from normal view to an outline of the bounding box of the object.
Does this help?