context finds files in the doc-folder of texmf trees. As an example:
This is LuaTeX, Version beta-0.60.2-2010100221 (MiKTeX 2.9) (rev 3736)
This can even give trouble during format generation as the doc-folder of circuittikz contains a "context.tex".
I could reproduce the problem (reported on the winedt mailing list) only after an update today where I updated only six miktex-XX-packages packaged on 15 and 16 november but it is possible that it existed already before unnoticed. The search path of luatex seems fine. Tell me if you think that it is a context problem, then I will make a bug report there.