Fans and Fan expansions

I’m being a little presumptuous here, but that’s me –
There are people out there using the world of Fletnern as their campaign world. Sometimes I interact with them, but not that often. As you would expect, they are developing things within my world, making changes, advancing story lines that I haven’t touched, etc. but the truth is, I’ve been living part time in Fletnern for about 30 years now, and I have good portions of the next 150 years (in game) figured out.
Why am I bothering to say this? Fortunately I have not yet run into this, but the day may come when some GM using Fletnern or some other thing that I have written will come back and insist that I stole his or her idea(s). It won’t be true, but they may not see that from their perspective.
What I’m saying is this – I hope everyone out there uses Rhum, Fletnern, Legend Quest, etc etc etc, but if you fear someone (even me) stealing your ideas, don’t tell people about them.
I was young and dumb once. I play tested some major games for a major company, and I shared all sorts of ideas with my contacts at the company. One of those “game designers” stole my ideas and published them, and because I was young and dumb, there was nothing I could do about it, well, nothing but start my own game company and outlast him. Because of my own issues, I flat out wouldn’t swipe material from one of my customers – maybe from a friend, but only after telling him about it.
So – You can trust me, but still, don’t tell me everything if you think there’s any chance I would “borrow” it. Don’t trust other folks either, not with the jewels of your creation. It’s tempting though. Gamers love to talk about games. You can tell everyone everything, but don’t get annoyed if one of those writer-blocked “game designers” decides that you’ve got better stuff than he’s got that month. Them’s the breaks!
P.S. - I’m no longer bitter about a 20+ year old theft. I really haven’t been for years - since the company he worked for went belly up. I Googled him though. Turns out that those who can’t, teach - Yep, he works at a college “teaching”.