Thank you for writing.
I was able to reproduce the issue and I am happy to inform you that it has been addressed and will no longer be present in our next major release. Until the next release you can work around it by handling the PrintCellFormatting event and adding the following code to it:
sender, PrintCellFormattingEventArgs e)
GridViewGroupRowInfo row = e.Row
" | "
I have also updated your Telerik points for bringing this issue to our attention.
I hope this will help. If you have further questions, I would be glad to assist.
the Telerik team