When constructing mechanical constraptions with subgrids (i.e. a catchblock) with the blueprint control block, catchblocks spawn with another subgrid attached to them, which goes all clangy and makes the block unusable.
Deleting the catchblock causes the below crash.
Because of this, I disabled the blueprint control block on my server altogether. Using it for mechanical things is currently impossible. I reported this to Keen over a year ago :P .

2020-11-01 09:51:18.834|Main Thread> Error: Attempting to deconstruct an unknown block!

=============================== FATAL EXCEPTION ================================
Exception occurred: System.ArgumentNullException: Value cannot be null.
Parameter name: key
   at System.ThrowHelper.ThrowArgumentNullException(ExceptionArgument argument)
   at System.Collections.Generic.Dictionary`2.FindEntry(TKey key)
   at System.Collections.Generic.Dictionary`2.get_Item(TKey key)
   at VRage.Scene.MyTieredComponentGroup`2.GetParent(TChildComponent child)
   at VRage.Scene.MyTieredComponentGroup`2.ChildOnParentChange(MyHierarchyComponent target, MyHierarchyComponent oldParent, MyHierarchyComponent newParent)
   at VRage.Game.Components.MyHierarchyComponent.RaiseParentChange(MyHierarchyComponent previous, MyHierarchyComponent current)
   at VRage.Game.Components.MyHierarchyComponent.OnBeforeRemovedFromContainer()
   at VRage.Game.Components.MyEntityComponent.SetContainer(MyEntityComponentContainer container)
   at VRage.Game.Components.MyEntityComponentContainer.Clear()
   at VRage.Game.Entity.MyEntity.Delete()
   at VRage.Scene.MyScene.DestroyInternal(MyEntity entity)
   at VRage.Scene.MyScene.CloseQueued()
   at Sandbox.Game.Entities.MyEntities.UpdateAfterSimulation()
   at Sandbox.Game.World.MySector.UpdateAfterSimulation()
   at Sandbox.Game.SessionComponents.MySessionComponentLegacyUpdateScheduler.DoUpdateAfterSimulation()
   at VRage.Components.MyUpdateScheduler.RunFixedUpdates()
   at VRage.Components.MyUpdateScheduler.RunUpdates(TimeSpan currentTime)
   at Sandbox.Game.World.MySession.UpdateComponents()
   at Sandbox.Game.World.MySession.Update(MyTimeSpan updateTime)
   at Sandbox.MySandboxGame.Update()
   at Sandbox.Engine.Platform.Game.UpdateInternal()
   at Sandbox.Engine.Platform.Game.RunSingleFrame()
   at VRage.Components.MyUpdateScheduler.RunFixedUpdates()
   at VRage.Components.MyUpdateScheduler.RunUpdates(TimeSpan currentTime)
   at Sandbox.Engine.Platform.MySandboxUpdate.<RunLoop>b__18_0()
   at VRage.Utils.FixedLoop.Run(Action tickCallback)
   at Sandbox.Engine.Platform.MySandboxUpdate.RunLoop()
   at Medieval.MyProgram.Main(String[] args)