Created attachment 83436 [details]
screen shot of my example

in former versions you could format the cell for [hh]:mm to add time values, for example flight times. it is not possible now.
In the example on the screen shot, you can see my columns and on top you should see the summary of the flying hours below. But the value shown is not right, I don´t know what it is calculating ..... 
The cells are formatted as "user defined - [hh]:mm" and as you can see, I do it this way since 2005 and it worked until now ......