DEFECT with SUM Data

I have found a case where SUM is working incorrectly.

Then I change the field "Time Spent Hours" from "Don't summarize" to "Sum"

Once this is switched to "Sum" the value changes from .50 to 11, which is impossible ot explain other than it is a defect.

Please help me with a fix for this as it prevents me from using powerbi for my being useful for summarizing this field.