https://www.youtube.com/watch?v=eQYsSOfXxuc
Take a factory 2 or factory 3 that is set to produce rocket control units. It doesn't matter if it already has modules in it. Control click speedmodules into it
*poof* now your entire in-hand stack is vanished and none go into the slots !!
It works normally for productivity modules
Hope this is enough to go on. Save attached in case it is something bugged unique to me.
