An example of a researcher being 'scooped' as a result of working openly? A reason that researchers sometimes give for not working in the open is the fear of having a publication 'scooped' by a competing researcher. Is there a clear, verifiable example where scooping has happened as a result of work being shared informally on the web prior to formal publication?

By being scooped, I am thinking of a situation where Researcher 1 has made progress on a project openly, but has not yet formally published her or his findings. Researcher 2 subsequently takes the informally shared work as a basis for a publication, to the detriment of Researcher 1.
The Kuiper belt object Haumea was perhaps discovered by a second group through looking at observation logs - it was very controversial. 

The controversy has a wikipedia article