Some shooters have experience a problem with their Race Master fit to their pistols. The following should help you resolve this:
First – check to see that the fit to the locking block is good. Remove the slide lock from within the block – and assemble the block into the holster without a slide lock. You will need to remove that long M3 screw from the back, and the slide lock will slide out upwards. Holster your gun and see that is slides in and out loosely. If not – you need you widen the groove of the trigger guard itself in the locking block. To do this, you can use a flat file, as shown in the attached picture, remove from the thinner side – not the side with the safety. you will not have to remove much, probably only a couple of tenths of a mm. Test to see that you have removed enough. when checking, place the locking block into the holster body, as that tends to close it up a little.
Once a good fit is achieved to the locking block – it is time to consider the slide lock tooth itself.
This has to fit well to the trigger guard of the pistol. if it is too tight – the gun my not fit in at all – or if it does – it may be too tight for a good release. you will need a light hand, and a dremmel tool – or a small file.
Look at this clip on youtube for some guidance on how best to do this: http://www.youtube.com/watch?v=EV0t-2bVu8w
If you are using a file, I would suggest removing from the lower edge of the groove, not the top which has a more difficult contour. again – you will not have to remove much, probably just a couple of tenths of a mm. the slide lock should slide on and off from the trigger guard without resistance, but should fit snugly, so that the gun cannot wobble in that notch.
Once you have done the above fitting, I am very sure your problem will be resolved.