In general, static methods are supposed to be thread-safe, and there's no warning in the docs about it not being so.

But TypeDescriptor.Refresh may end up calling into ReflectTypeDescriptionProvider.GetPopulatedTypes. It does so while holding a lock GetPopulatedTypes enumerates the _typeData Hashtable. If a concurrent call to GetTypeData (which takes a different lock) mutates that hashtable, it invalidates the enumerator being used by GetPopulatedTypes, causing GetPopulatedTypes to throw an exception.