I don't know if this is a bug or a recent change to this, but I thought I'd report it anyways...
In phpBB 3.2 if you click on Active Topics and there hasn't been any new activity for a while, it will not show the "Display and Sorting Options" at the bottom of the page results in order to select a later date like 2 weeks, a month, a year and etc.
See screenshot 001 to understand what Option drop-down is missing. (screenshot taken from phpbb.com)
See screenshot 002 to learn where the above option is located. (screenshot taken from phpbb.com)
See screenshot 003 to see results from phpBB 3.2 when it could not find any recent results under Active Topics – notice that you can't find the drop-down option. – sorry my site is currently offline.
This doesn't happen to phpBB 3.1.10 – it will still give you this option even if the first results were empty.
See screenshot 004 to see results from phpBB 3.1.10. You can test this yourself in my current active phpBB 3.1.10 forum: http://www.my15birthday.com/forum/search.php?search_id=active_topics
Note that my custom theme inherits from prosilver. So those templates are intact – nothing has been edited in those HTML files.