Autosum sums entire column instead of selected range

[excelhatesme2]

Say I have this data:
\1

I select B75 to B77 and hit Autosum, all good:
\1

I select C75 to C77 and hit Autosum, all good again:
\1

I select D75 to D77 and hit AutosWOAH WHAT'S GOING ON
\1

With D it's grabbing the entire column above my selection and trying to place the result in D75, I think.

I know I could just manually type the equation to get the sum I want, but why is Autosum being so annoying in this one instance?

(Excel 2010 btw.)
(Couldn't work out how to make those screenshots show up. One of those days.)

[jhuang5132]

I'm not really qualified to give an opinion, but I think it's because of the colon (or more specifically because it is in time form).

[easyexcelanswers]

sumoftime.xlsxIf you select the cells in "d" and format them for time, the auto sum will work