Copyright issues are really confusing and people printing articles on copyrights or issuing statements about them make it more confusing. I came across this website once, out of curiosity, and it turns out a lot of what you read is incorrect information.
http://www.tabberone.com/Trademarks/trademarks.shtml
I’m not affiliated with them but they’ve fought for their rights in a federal court of law several times, even though they are not lawyers, and seem to have some experience with these kinds of things. Basically, what it sums up as, is you have the right to the pattern you develop and print, including photos and graphics, but quilt blocks and patterns themselves cannot be copyrighted because they are a useful item. So go ahead and post your instructions, it doesn’t infringe on anyone else unless you use their photos or original work.
Of course, this is just my opinion and will probably stir up the pot more.