Yes, I think so, on the stuck resources. Certainly if you cancel a constuctors build order after giving it but before the constuctor loads the required materials then those materials will remain reserved (for rest of game, I suspect). I've never actually tested the mid-construction cancelation though.
I posted about the fuel cancelations in a thread a few months ago (when we had all those resource discussions...) but I could not find it. The problem arises when the fuel reserved by one ship is used by another. In my experience this happens when freighters grab fuel already reserved for military ships. The reservations for those military ships are then canceled when the military ship is on approach to the refueling point and it returns to no orders (with no notification it might be added).
[A common example I encounter - I establish a new colony and have a couple of ships guarding it for arrival of the colony ship. Shortly afterwards I send out a couple of system defence frigates to free up my longer ranged colonisation fleet. I send out the SD frigates to the new colony with a refuel at colony order (since they have minimal fuel tanks and I want them ready if needed). So the reservation is made for, say, 2x180 caslon. Now its a new colony with 2000 fuel, take away 1000 some silly freighter wants to ship back to my home system (which already has 2 gas mining stations cranking it out...) and take away maybe 500 to refuel the colonisation fleet. So things are getting a bit tight, say 500 caslon left with 360 reserved for my incoming frigates. Okay this sets the scene...
What happens next is that a couple of freighters arrive for tranport missions either delivering for a rudimentary spaceport build job or carting away resources (fuel or otherwise). Now they fill their tanks. The first one, for arguments sake, takes 250. Yep, it does that even though there is only 140 unreserved fuel. So now there is 250 caslon and 360 reserved! Except there won't be as one of the two frigates will on arrival cancel its reservation (automatically, unnotified). If another freighter comes along and takes 100 fuel (which it will do ignoring the existing reservation by the frigate) then both frigates arrive in the system approach the planet (don't quite make it to the gravity well) and cancel their orders to drift off into the system, usually pretty much out of fuel... THAT is not a robust reservation system...