That's very common, actually.
A substance melts, but the recrystallisation from the iostropic melt can be kinetically inhibited. If you cool further down, a less stable form of the same substance, with lower melting point, can crystallise, and re-form over time, into the original phase.
This (according to Ostwalds rule) happens practically every time a suitable, less stable polymorph exists. Or let's rather say there is a general tendency for it to happen.
Another, very common example (to which Ostwalds rule also loosely applies) are polymers. Because of their chain structure, crystallisation (if possible at all) is much inhibited and usually never occurs until you cool a good ten K or so below the equillibrium melting point.