Lauren and I just checked this, and it happens here, too. That looks like a bug! I’ll report it to QA in a few minutes.
Well, it can be an issue if you use a different version of the engine from what we have. We used 4.10.4 on the stream, not 4.11 Preview 4, so that could cause errors. However, in this case, it’s a legitimate engine bug. It is worth noting that since the game re-instantiates all objects on startup, your tank in-game (including PIE) should be fine, and should have only one child turret, even though it will have more than one in the editor.
We do attempt to stay on top of threads, but some posts may fall through the cracks, or may be addressed by other people like community members or other Epic staff. We’ll see if we can improve that. Thanks for your feedback!