grammaticality - Why do some people say "there have voted"? Is it grammatical, or maybe historical?

This is in fact a legitimate construction, though formal and old fashioned, and limited by certain conditions not all of which I am fully aware of. Consider this quote from the standard modernised rendering of the Declaration of Arbroath, the famous declaration of independence of the Scots in 1320:

In their kingdom there have reigned
one hundred and thirteen kings of
their own royal stock, the line
unbroken by a single foreigner.

This construction is a case of balance inversion, where putting the subject in first position would result in a very late position of the finite verb, which is often considered uncomely and ponderous:

*In their kingdom, one hundred and thirteen kings of their own royal
stock, the line unbroken by a single
foreigner, have reigned.

I agree that the "there have reigned" construction is rare and out of place in informal language, and unnecessarily pompous in short sentences. It is probably a matter of tradition in your case, since this exact formula is standard in the House of Lords, as Nico has mentioned.