Hi,
i know these problems were already mentioned a couple of times, but i havnt seen them on the new forum. Also i dont know if relic is working on these problems or not, but mines cannot be canceled during the build. They can be destroyed but its not possible to cancel an unfinished mine and refund its price.
The other problem is the unfinished barbed wire. You cannot destroy any unfinished barbed wire by gunfire. Basically its easier just start to building it than actually finishing it.