Reverse Heist/'plant item' issue- item disappears on early area exit

Is this by design to keep you from leaving the area without planting or leaving the item first?

If it's by design it would be nice to get a warning that the item will disappear if you leave the area early.

Last week it happened to me with Karst's poison lockpicks. Went out to dump stuff and when I got back in to the end to plant them they were gone from my bag. Exact thing just happened with Tullina's engagement ring as well.

Bug or intentional mechanic?