I have a project I've been working on for a long time, and randomly today one of the designer.cs files is behaving strangely.
The following screen shot shows how the icon in Solution explorer does not appear as it should do.

When I open the corrupted frmCase.Designer.cs file all my code is there, but I notice that intellisense is not recognizing objects

Contrast with another Designer.cs file where intellisense colour codes the objects.

I have no idea what this has occurred, or how to rectify it. Could anyone please help me with this.
partialkeyword from the class definition header still there?