Grouper function worked with json file, but does't work with oData

Hi folks

I copied one javascript code from a sample application, it was working very well when data were retrieved from json file, now the data have been retrieved from oData and the group function does not work anymore. It does not have a java script error, the list is sort is changed, but the result is wrong.

The list before groupping:

The list after the groupping:

how you can see, the lines with "1800" were not grouped, but the sorter were changed

file masterview.xml:

master.controller.xml:

Grouper.js: