I don't know why you discuss the matter but my initial question was if it is a bug that normal and improved silos can be upgraded to level 6 and I received the required answer. Thanks Ravel for the information and I hope you'll be here for us with much more frequent status updates to various topics that bother us.
@CrazyBat andBrayar: Please find another thread to clarify the benefits of using silos, cars, boosting sales and stuff![]()