If it was fully charged (noty likely) it's abnormal... Theoretically, if the pack was fully charged, it'll take about 5-6 hours discharging them at 0,5 amps... Discharging at one amp, should take about 2,5-3 hours.
Personally, I've always charged my NiMh AA's with 1 amp/discharged at 1 amp. Works fine untill they get very old... But NiMh's definately dont like being stored for prolonged time.
How old is the pack? Has it been stored for a long time? What brand? Might there be some bad connections in the setup? Do your charger work fine with other NiMh's?
Do you have a separate voltmeter? If there's one bad/dead cell among them, this particular one would likely have significantly HIGHER voltage during charge and significantly LOWER during discharge...
If you dont have a voltmeter, you could try charging and then discharging the cells one by one - provided your charger support charging single cells. This might prove if it's only a few or all cells having problems. Do take a while of course, so the next suggestion might work easier
Another option could be that you could leave the pack on trickle charge for 3-4 hours, and then try a regular charge...