Suppose a Tremere parens holds the sigil of one filius, but the filius moves to a different Tribunal (e.g. Novgorod) from that of the parens (e.g. Iberia). It would seem that the parens has now a vote in Iberia, and one in Novgorod - which may be inconvenient in terms of going to vote, but more importantly does not really "compact" the votes into blocks for tribunal voting but instead increases the number of tribunals in which an elder Tremere may meddle.
Is this really the case? If so, does it mean that a parens will usually discourage filii from moving to another Tribunal? If not, do elder Tremere "trade" sigils to retain blocks - perhaps if you hold a sigil from another Tribunal, you are required to assign it to an elder Tremere of that Tribunal?
A similar situation came up in my saga. I was going to rule like Xavi mentioned above, but the feedback I got from this forum then, was that this would break the "True Lineage" concept... (Admittedly, in my case, it was not a pater in a foreign tribunal, but a disappeared/Marched/dead pater)
Still, I gnored the advice because I decided it would be more fun for the saga to have the PC junior Tremere being meddled with by a local senior Tremere (Rotgier of Montverte)
Yes, the vote gets sent to the senior Tremere in the tribunal, or in some cases, to the senior Tremere in a neighbouring Tribunal. As an extreme example, Loch Leagan, Stonehenge, Ireland and Normanday all have the same guy as boss of the Tremere. This guy is called an "exarch".