The below excerpts are from the D&DI Compendium entry on "Short Rest", referencing PHB 1.
No Strenuous Activity: You have to rest during a short rest. You can stand guard, sit in place, ride on a wagon or other vehicle, or do other tasks that don’t require much exertion.
Using Powers while You Rest: If you use an encounter power (such as a healing power) during a short rest, you need another short rest to renew it so that you can use it again.
It seems apparent that you can use powers during rest periods as well as other non-encounter situations. However, while the rule does specify that you cannot perform "strenuous activity", it doesn't seem to state whether power usage falls into that category.
If you do decide to use a power during your resting period, do you have to take another rest period to gain the benefits of a short rest, or do you just add more time to the same resting period?
Or, is this really a negligible issue, since most powers take only 6 seconds (1 combat round) to use?