Yea it happend to me something like that. On "Endless mode" the enemyes can move on all tile. If you like the normal gameplay just play "normal mode". But It happend to me on "Endless mode" when I built a tower and the enemyes come to pass over that tile... most of the time they change the way, but sometimes they just dotn stop to walk ower my tower. I hope that this is not the idea of that mode and think they shouldn't do this. 5 or 6 enemyes pass ower my tower. They act like there has no tower.

They should only pass over towers in one of two necessary conditions:

1. There is no viable open road path for the enemy to the base. In this case it will pass through the minimum number of towers necessary (generally only possible in 5.8 or custom maps)
2. You've built the tower after the enemy spawned. If it were possible to change an enemy's path with towers after an enemy had spawned, players could "bounce" enemies back and forth in a path forever. So once an enemy is spawned, its route is set, even if you later build a tower in the way.

... which is to say, I don't really think this is an actual bug

EuphoRowan is completely right, and there's no bug. Hardcore mode = enemies walk on platforms.