does anybody know about shimano deore rear deraillers? I purchased one

[tommartella1]

from a bike shop on the internet.? I have a 9 speed mountain bike with shimano deore components and needed a new rear derailler. I received the new derailler and brought it over to my bike shop to install. It looked identical to the one I had on my bike with a curious difference. He said the new derailler had a reverse spring which means when I now shift in higher or lower gears I have to shift in the opposite direction on my shifter levers that are on my handle bars. I have rapid fire index shifters. The model # of the new derailler is rd-m530 long cage. My bike mechanic said he has only seen this reverse spring on giant bikes. Is there any adavantage or disadvantage to this particular reverse spring derailller. Did the internet bike shop send me the wrong derailler. It seems to shift ok except getting used to having to shift in the opposite direction.