robzilla - 7:37 pm on Oct 19, 2008 (gmt 0) Correction: I did not have Search Type set to Web Search this time. As soon as I did, the old percentages were back.
then you only need to be in first place for a single search a day for this to happen
If that's the case, the position reported should slowly (or radically) decrease over the next couple of days. So far, it hasn't, but I do see the percentages going down - 25% for impressions, 10% for traffic (compared to the previous 50% and 20%, respectively) [see correction note below]. The "1 week ago" label I also find confusing as, to me, it implies that it's displaying data from 7 days ago, not necessarily from the last 7 days. Unless I take it very literally and replace "ago" with "past" and thus interpret it as the last 7 days gone by, which is probably what they mean.
Correction: I did not have Search Type set to Web Search this time. As soon as I did, the old percentages were back.