Not 100% sure this is a bug or not and I hope I can explain it clearly without spending a bunch of time doing screenshots. It has to do with the Committed amount in Manufacturing Central. If you have child variable products set to unmanaged stock the Raw Materials listed in the Bill of Materials will set that Raw Material's "Committed" amount in Manufacturing Central to the "Total in Warehouse" amount. This works according to design I'm assuming.
Where the problem is if you have a variable child product set to "Manage Stock" and has a quantity greater than zero and the Parent Product not set to "Manage stock" this will also make the "Commited" amount of the Raw Material in Manufacturing Cenral equal to the "Total in Warehouse" amount. One needs to have the Parent of the variable product set to Manage Stock not just the child variations in order for the "Commited" amount of Raw Matterial to be tallied accordingly. Maybe this isnt really an issue other than one doesnt really Manage stock of the parent of a Variable product yet by requiring the Mange stock to be turned on a "Stock Quantity" of 0 is displayed hopefully has no ill effect on other aspects of ones inventory. I have no indication that it does so far.
Hopefully my explaination isnt to confusing.