Steps to reproduce:
1. Go to http://www.spoj.com/problems/classical/
2. Click any tags on the right (dynamic programming for example)
3. Click "Challenge" on the top
All problems on challenge section with dynamic programming tag shows.
What actually happens:
All problems on challenge section shows. Tag is gone.
While we're at it, this message is also misleading
You can share a subset of our problems with your friends using the link below:
since all problems in that tag is in riddle section. It still shows that even if you manually change the url: