Weird phrasing in the rules, between them it's clear that:
1. Units must be released from reserve mode to use air transport in the exploitation or reaction phases.
2. They must already have been oriented toward Move mode under the reserve counter as they cannot change to Move mode if in Combat mode.
3. If they are released reserve, they can do their 1/2 MA in exploitation or 1/4 MA in reaction phase.
I suspect the weird wording is to cover the case where a Move mode unit is in an airbase hex and moved by air during the exploitation or reaction phase. Such a unit would not have the ability to move either before or after air transport. And that's probably the reason for that weird phrasing in 14.9d.