I've tested it and it works for me. For avoiding empty columns I've used the same trick that I use at jacket (kovid told me so when I asked about the same problem:
Code:
<div style="display:{_vts}"><b>Series 3:</b> {_tse}</div>
With _vts a custom_column with value 'None' if _tse is empty.
And I know I'm greedy but... in the same way you send the series when you update metadata, could you send the comments if 'use template' is activated?