Unexpected Behavior from Worksheet to Unembeded Chart

Preliminary "explanation" before the problem.
I keep track of my gas mileage via a spreadsheet and three corresponding clustered-column charts (Gallons, Trip Miles and MPG).
Nine column-values are the most eye-pleasing.
Problem: I just filled up last week and was going to add the new data.
Column Headings:
DATE, GALLONS, PRICE/GAL, FUEL SALE, ODOMETER, TRIP MILES, MPG
I have formulas to compute FUEL SALE, TRIP MILES, MPG
Rows:
Fill-up dates (total 9 per chart)
(If I'm on the first row of a new worksheet, I label the rows alphabetically B through I; and insert interim numbers to raise the chart columns above the X axis.)
PROBLEM DESCRIPTION
I'm ready to add last week's fillup. Before adding, each chart displays the dates properly (Date #1: 25-Jan through date #8: 25-Oct)
When I replace the interim "I" in cell A-10 with 11/29 (formated to 29-Nov), all three charts end up with two extra dates and are formatted in Mmm-Yy style (Jan-07 through Nov-07).
I'm thinking I must have a box checked which shouldn't be, or vice versa.

Thanks ever so much,
Stumped