The previous KendoUI mobile listview respected datasource grouping when endlessScroll was enabled. This functionality has regressed in the Q2.2013 release.

An extract from my support ticket 718079:

For our application, it is not acceptable that the ability to group with endless scrolling has been lost. Grouping is fundamental to the user experience in our app - especially when there can be a lot of items in a listview. It is just as important as the performance that endlessScroll enables. One, without the other is a backwards step.

Telerik response extract:

Thank you for your feedback. I fully agree with you - grouping of a large dataset improves the user experience and provides the necessary visual clues for the user to determine the current position in the list. The only reason why this is not supported is the high complexity and performance implications of the task, when combined with virtual mode, which is a requirement for a large list support - our previous implementation easily crashed the mobile browser when 100+ items were displayed. I would like to suggest that you post this feature request to our UserVoice feedback  site; we are actively following the popular items and responding to our customers demand with each release.
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I do not believe the complexity is quite as high as has been described. The datasource can identify how many groups there are - for any current filters and adjust the endlessScroll height accordingly. The listview items themselves can be adjusted down in position by the number of group headers above them.