odftoolkit ignores data of group rows

[Frank Ho]

Hi, All
    I have next ods file :           row 1   value1row 2   value2row 3   
value3row 4   value4row 5   value5
if I add group for row 2 to row 4 (Data -> Group and Outline -> Group), then 
when I use getDisplayText(), it cannot read data of row 2 to row 4, and 
odftoolkit will take row 5 as row 2.
if I delete the group, then all things back to normal.
Is it a bug?
Thanks