The screw for the spring is actually one of the biggest problems on the cheap adapters - it should be just about flush, but is frequently sticking out where it can snag on the mount. Besides the spring, the machining on the cheap adapters is frequently not as good as the genuine Pentax. Check for burrs on the ends of the bayonet flanges. You may also want to compare the flanges to a K-mount lens to make sure they have been machined to the correct widths. If you have removed the spring and screw, and there is any sort of scraping sound/feel when installing the adapter, something is sticking out and needs to be removed.
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