Over the years I have never had any issues with flat spotting street tires or race slicks.
Having said that, tire compositions have and are changing recently. For example this summer at Mosport Race Track a Pirelli rep told us that motorcycle sport tires now have next to no rubber in them any more and as a result they will crack in cold weather such as below freezing temperature.
I saw a newish front Pirelli tire that looked like it had been cut by a razor across a tread block all the way down to the base of the tread. The tire had been on a friend's bike last winter which had been stored in an outside tin shed, unheated. The Pirelli rep said they have seen this often. The compounds in modern motorcycle tires do not like the cold.