Thulkkonen,

You might want to make sure that

A. your tensioner is the latest one (do a search, there are three versions)
B. It is installed properly.

If something is wrong with either A or B, the chain could easily jump to the position you described. The last time I took mine apart, I don't think there was enough slack in the chain to do what you described (i.e. just removing the top guard and moving the camshaft).

Then again, I could be off the mark. I'm the silly bastard that dropped the washer down the chain box...

cheers,
dan r.