I already answered your support ticket on the subject. For convenience I will paste my answer here as well:
Indeed we are aware of this issue and it is already logged into our Feedback Portal for fixing. You can track its progress here: GridViewNewRow is not displayed if NewRowPosition is set to Bottom,RadGridView is placed in a container measuring its children with infinity and there are no items.
Unfortunately, I can not suggest you another workaround for this. We are sorry for any inconvenience caused.
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