What you're seeing is a reasonably well-known display error.
In essence if your DR rating (S, A-E) cannot go up to the next level because it is prevented from doing so by your SR rating (S-E), it continues showing the lower rating while the bar itself shows your progress through the higher rating.
What has happened to you therefore is your DR has dropped from A rating to B rating (above 30,000pt to below 30,000pt) and as your SR has also dropped to B rating you cannot advance to A rating again - but the bar has continued to display your progress through the A rating (about 32,000pt, or 10% through) - making it look like you are at the bottom of DR B because the rating shows you as DR B.
You are effectively high enough to be DR A but you cannot be DR A because you are SR B, so you're shown as DR B but your bar is acting like you are DR A - thus you are at the beginning of the bar appropriate to A (at about 30,000pt) while the rating continues to display B.
The change from "bottom of B" to "end of B" reflects the fact your DR has dropped in the next race and you are now DR B (at just under 30,000pt).