  In systems with broken $U(1)$ symmetry, such as superfluids, superconductors
or magnets, the symmetry restoration is driven by proliferation of topological
defects in the form of vortex loops. Here we discuss that in certain systems
the proliferation of topological defects can, by contrast, lead to the
breakdown of an additional symmetry. As a particular example we demonstrate
that this effect should take place in $s+is$ superconductors, which are widely
discussed in connection with the Iron-based materials. In these systems a
vortex excitation can create a "bubble" of fluctuating $Z_2$ order parameter.
Thermal excitation of vortices then leads to breakdown of $Z_2$ time-reversal
symmetry when the temperature is increased.
