Playing on TRADE_FUZECRAFT_V9. This was from earlier this morning. Don't know why they would put an Upgrade Station without putting a credit box in the UI or at least making the game drop credits when you kill someone, BUT...
http://steamcommunity.com/sharedfiles/filedetails/?id=257714014
You're allowed behind the Upgrade Station because the actual prop for the Upgrade Station has an opening on the top that Valve never bothered to fix.
Don't know why they would put an Upgrade Station without putting a credit box in the UI or at least making the game drop credits when you kill someone, BUT...
Map design. Also, letting credits drop from people and then upgrading your gun would be overpowered as donors could just kill non-donors and upgrade their guns.