As any designer will know the issue of design and intellectual property theft is one that affects all of us. It's a very tricky subject because it is very hard to actually prove and is an emotional hotspot, that more often than not is learned the hard way.
I have heard of a fair few stories of small designers who have had their idea's nicked and put into production by other people, sometimes big corperaions who have not paid the designer for the original idea. I've also heard stories of young enthusiastic designers going to job interviews and being asked to produce a mini project or moodboard for the company to keep only to find the position taken even before their interview and their hard work being used by the company.
In an ideal world a designers intellectual property is acknowledged and protected, in fact it is...but only if you can prove that the comptitors design is at least 90% similar and you have relevant documentation date stamped to show you did it first.Maybe it should be more pertinent to say that in an ideal world there would be no-one who would want to nick your idea. But, we don't live in a world like that.
The bottom line is that prevention is better than dealing with the consequences. Copyright is a very convoluted thing, but do make sure that you copy your designs and post them to yourself leaving them unopened with a postmark should any future problems occur and if you do share new methods of construction that you patent the process. If you think you have a killer idea don't discuss it with anyone until you have it in production. If you feel that this has happened to you seek legal advice to nip it in the bud.
For further information:
What is Copyright