The copyright applies to the pattern and to the instructions, not to the quilt that you make from the pattern. This means that you cannot claim that the pattern is yours, sell the pattern, or enter the pattern in a quilt show as your original design.
Some blocks and quilt designs are part of quilting culture and belong to everyone. Others are original to a specific designer, copyrighted or not.
If someone has taken the time to apply for a copyright, then they can sue for damages, if you publish or claim their pattern as your own. If it isn't copyrighted, then it becomes a matter of personal ethics, plagiarism, and not a legal issue.
When someone else's idea sparks creativity in you and you make it your own, then the resulting pattern is yours. Typically changing about 25% of a pattern is considered to be enough change to make the pattern new and yours. In this case, someone should not be able to look at your new pattern and say, "This quilt pattern is exactly like so and so's quilt pattern." If you have any doubt about the significance of your changes, use the inspired by .... on your new quilt pattern.
In my opinion, the answer to the original question before us is not about buying the kit; one cannot copyright what fabric must be used in a quilt pattern. The question is about the pattern, and the solution remains in examining the quilter's intent.
Does the quilter intend to copy the pattern or is this pattern a source of inspiration? The answer to this question is the answer to the question, "Should I buy the pattern."
I hope this makes sense to all who are worried.