So, it seems that when you attempt to remap the keys (because i was used to using F5 and Ctrl F5 to buy / sell metal and F6 / Ctrl F6 from the original settings, and wanted to put them back), it doesn't seem to accept the new mapping correctly.
Here's the steps I went through in the game (not all are probably necessary, but just in case):
1. Start a game on a random medium map with 3 normal random opponents.
2. Open the key mappings screen
3. Click on "Open network status window", then click 'clear', then 'add', and press the F12 key to remap that one to F12.
4. Click on "Buy Metal", then 'clear', then 'add'. Press the control and F5 keys at the same time. The screen will now show the key mapped to "Ctrl+Ctrl". Screen shot attached.