Mine have been crazy for the past week. All up and down the first page for my keyword (not over 5 though unfortunately).
It's normal and it's called the "Google Dance" while there is a lot of updates going on like and the big G have just updated the BL and they are exporting the PR to the toolbar... so alot of DC is going on/off all the time. Just wait till the PR is totally exported and it's going to be more stable.
It's normal. Given all the updates that's going on, seeing things like this will be common until it's all finished. Lots of "strange" things happening in webmaster tools by google, googlebot slow in indexing some sites and things like that.