Ahh...I see what is happening here. Most groovy fields are automatically converted into properties by the compiler. The content assist engine prefers to show property proposals over field proposals. So, it tries to filter out all field proposals that are duplicated by a property proposal. It looks like the field proposal for VALUE1 and VALUE2 were being filtered when they shouldn't be.
The behavior that I am seeing is different from what you describe. I see that VALUE1 and VALUE2 are never proposed regardless of the existence of the parens. Is this what you are seeing, too?