Also, if you open a different window to the lease/buy screen, it will release all other holds that you have. Thus, for example -
1. Find 2 planes you want
2. Open both in a new window/tab
3. When first window opens, you have it reserved for you.
4. When second window opens, it becomes reserved for you, but your reservation drops on the first plane.
5. You go back to the first plane and can still lease/buy it, as long as noone else reserves/leases/buys it before you.