Hi,
In my case it is working all the time so far but I know this answer doesn't help you. Many SEO's facing the same issue. I am quoting Google's John Muller's on this
"Just to sum up the possibilities ... As others have mentioned, Sitelinks demotions are demotions, not removals, so what you're seeing might be as expected (also, the changes are not immediate).
If you'd like to have text removed from the snippet, there are a few possibilities you might want to look into:
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use the "nosnippet" robots meta tag
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use an image (as others have suggested)
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use a robotted JavaScript file (also mentioned above)
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use a robotted iframe
The "googleon" / "googleoff" tags are only for Google Search Appliances (so if you're running your own, local search engine), not for web-search."
You can read full discussion here @ https://productforums.google.com/forum/#!topic/webmasters/X1SluyGID9o/discussion
Hope that helps.
Thanks