My 7th lvl Cleric has been using this spell of late as he's been one of the main offencive mambers in his parties of late. The spell has a duration of 1 hour/level but always seems to cut out after what would be maybe one or two. Dont know if anyone else is having the same problem or not.

This isn't a bug. GMW has been reduced to turn/level instead of hour/level, in your case making it last 7 minutes instead of 35.