It's time something was done about the problem.
It is a sentence from Murphy's "Grammar". Using was confused me, for me it should be were. It looks like this clause is in subjunctive mood—something that is unreal / imaginary, and in that case you always use were for any object.
Unless, of course, it is not the subjunctive mood, what would knock me down.
Best Answer
As @tchrist's Google Ngram shows, it is established idiom, beyond the reach of mere grammatical logic.
And anyway, it's mandative; if it were subjunctive, it should be present subjunctive, It's time something be done.
ADD:
Jespersen, A Modern English Grammar on Historical Principles, Vol 4 (I omit notes indexing citations.):