Thank you very much for bringing the erroneous behaviour in keyboard navigation of the Kendo UI Spreadsheet to our attention.
I was able to reproduce the issue by following the steps outlined in this ticket. I have logged an issue and assigned a developer to investigate the cause. You may follow its progress at:
Once the developer can commit to a deadline, the milestone of the issue will be changed.
As a token of appreciation, I have updated your Telerik points.
Telerik by Progress