He probably means the multiple midway points patch. Anyway, the reasoning is basically the same, except this is for a custom block and not the original midway points.
Basically, the issue is that you are inserting the custom blocks as direct Map16 tiles, rather than part of an object. Objects are basically structures of Map16 tiles, and as part of defining these structures, you can specify what Map16 tiles to use based on conditions (such as whether the midway point is active). Direct Map16 tiles can't do this; for instance, you can see the issue in the original Map16 blocks with the switch palace blocks:
Thankfully, the multi-midway patch already comes with an object (appropriately named "multi_midway_object.txt"). This is intended to be inserted with ObjecTool. Read the readme for that patch, or this tutorial, for how to use it.
Thank you, but objecTool is still difficult to understand.
Probably because I don't know about ASM.