Withered bug?

Most of the time the effect of withered (2 set items) seems to work correctly, but in long bonus rounds some creeps were not throw back. therefore they get stunned or throw back just a little little bit... this seems to happen not everytime but it happen to me always in long bonus rounds and i saw this "bug" on boss and air creeps this is pretty annoying because this is the reason why i lost my longest bonus rounds