It's a screen redraw issue. Click twice W (without selected text tool) to update the screen.
Clicking twice "W" key will not update the text variable.
I think it's a problem with the new mercury engine in InDesign CC 2015.
It's not a new problem, I've seen it since text variables were first introduced (in CS4 I think it was): the only way to update a variable's displayed value was and still is to change screen mode.
I know that, in previous versions of InDesign CC 2015 we update the variables using the preview.
The issue is in the actual version, it's not working because when you change the again to the normal view the variable will return to the previous state.
Please make the 3 steps above to test yourself. I tested in Win and OS X and have the same result.
Ok, I understand (what you now describe wasn't clear (to me) in your original message). So things have gotten worse.
It's not the variables that aren't updated. When you apply a drop shadow in a text and for some reason you change the formatting of text (type, size, font,...), the shadow remains unchanged, even if you use the preview mode.
The only way I know to update the drop shadow is to change the display performance.
I have the same problem. What's funny is if I go into presentation few, I see the changes. When I go back to normal I don't.
Sometimes, pages at the end of the document change. Very frustrating. CS6 was fine for me. CC give me trouble.
I happens on other computers with CC with either Windows 7 or Windows 10. So I would say it is a CC bug. I did report it.
Hope we get a solution.