Line Graph Time Duration

[Randel2001]

i am trying to chart minutes:seconds week by week for a run of 12 weeks.  So wk1 30min27secs, wk 2 32min35secs, etc.  When I initially format the chart data as [h]:mm:ss it works although the formula bar still shows a date(?) but when I copy 11 weeks and paste above line 12 and update line 12 with the latest week, it changes the format even though when i go to format that cell, it is the same as above. 

[#2]

@Randel2001 

Where exactly format is changed and on what? In your file all looks correct except one cell which is entered as text, not time.