I had something similar happen to me although I didnt have any money invested in research.

My tree is still fairly small and most of it so far is through questioning family members for info. My problem is my mothers grandfather died when she was very young and that side of my family is lacking. I have posted various messages to various message boards over the years and found a woman that may be a relative. She sent me some names from her tree and some basic info but not enough for me to connect any dots. We exchanged emails for a short time but she just stopped responding to me.

Periodically I do a search online for surnames in my tree on the various websites and on one of the sites I found she had incorporated my tree in to hers. I know this becuase she had people from my fathers side of the family in her tree. I can only guess that she mustve downloaded one of the trees I uploaded to one of the websites.

I emailed her about this but never received a response from her.