general comment on adding items to and removing items from inventories :
vanilla factorio usually takes items from the last slots in an inventory first and adds items to existing (non-blocked) stacks first and then creates new stacks at the start of the inventory. thus over time all the items in blocked/red/limited areas are used up until the inventory has items only in the first "allowed" slots. this is probably the behavior that most people expect nowadays ...
but many mods search for items to take from an inventory by looping through the inventory from the beginning (or using api calls? i am no modder) and thus don't take items from the restricted end. new items then of course can be put in the inventory at the beginning, which seems to never use/empty those last items. this behavior might not strictly be "buggy", but is an annoying feature. to get rid of those items in restricted areas we need to either move them manually to allowed slots, or temporarily stop new items from being delivered to that inventory so that all items are used up.
it would be nice if all mods could show the normal vanilla behavior of taking items from the end and adding items at the start of inventories. without an api call that allows this behavior and/or modders not knowing about such api calls and instead looping through the inventory themselves (aborting the loop "when first item found" to save time/ups on large inventories), we encounter this non-standard behavior all the time :-(
my personal "fix" for this kind of problems :
in most of my maps, i try to hurry for logstics to be able to wire up inserters and chests. from that time on i no longer restrict any inventories by marking an area "blocked" but instead use conditions on the inserters, either simple conditions like "gears < 500" or a constant combinator with a negative amount (eg "gears -500") and even simpler conditions like "gears < 0", which also enables two more tricks: having one central constant combinator to change the amount of items that is stored in many different chests all over the factory, and/or using positive amounts of what i want to have and subtracting the chest contents, to use filter inserters with "set filters" (activating them only while the chest has less/negative items than the given positive amount).
