Parts disappearing but features still “selectable”.........

I have an issue, with a single part.

I will have a part open, The part Is open on its own, in a drawing, and in an assembly.

I will open the part – and begin to click though the features on the tree.

The part disappears if you go to edit a feature.

The part will then disappear; you can still see the planes, and the outlines of the features you highlight.

So I just close the part, However it has also Goes in the Assembly and in the drawing I have to close them all (without saving and reopening)

Its so frustrating as I need to change some fillet rads as soon as I click on the feature to edit it in the “preview” the part just disappears.

This is in SP5.