As a slight epilogue to my previous post Alterative Vote: What does 50% mean? I've remembered at least one unusual version of AV from my days of counting students' union elections which had its own definition of 50%.
Back in my days at the University of Kent the students' union (known as "Kent Union") used a version of the Alternative Vote with some quite unusual features. I got the impression that the rules used had been written by someone who either didn't really understand the system or else was trying to impose their own philosophy onto the voters.
By far the most inexplicable rule related to the "Re-Open Nominations" (or "RON") option. In almost all other versions of AV I've seen, RON is treated like any other candidate. But in the old Kent rules someone decided that it was wrong to transfer votes to and from RON - you could either select the RON option or express preferences for candidates but not both. RON's fate was decided in the first round of the count and it merely had to outpoll the candidate with the highest number of first preferences, regardless on the numbers involved. Otherwise all RON votes were set aside and the rest of the election proceeded without it. This nonsense has long since been abolished.
In the rest of the count it was not unusual for a lot of votes for excluded candidates to fail to transfer (or "exhaust") and so the winning candidate could get elected with less than 50% of valid post-RON exclusion votes. And there were even times when a candidate had an unassailable lead before the final two - they might have 45% of all the votes, one opponent 20%, another 15% and 20% exhausted. Under any other AV system they would be declared elected there and then, but for some never explained reason the Kent rules (or the person interpreting them) required the count to continue until the candidate had achieved 50% (even with two or more opponents) or all other candidates were excluded. This could result in pointless additional rounds in a count that added nothing to the outcome.
The idea seems to have been to ensure the eventual winner had the support of at least 50% of those voting (excluding the RON voters) but it made no difference to the outcome and in any case very few people paid attention to the actual voting figures. It also didn't really address what would happen if the winner didn't have the backing of 50% of those voting, and a new election would have made little sense when that very option was on the ballot paper and rejected. In practice in a close final two on transfers the winner indeed lacked 50% but this made no difference anyway.
Fortunately in a subsequent constitutional rewrite attempts to re-invent the wheel were abandoned and standard rules imported.
One other bizarre case came in elections for the University of London Union. These saw frequent problems and frustrations despite (or more likely because of) a permanent returning officer and the rules followed could often change from year to year. In general the ULU rules treated the RON option like any other candidate but in one year someone decided that RON could not be excluded and thus the entire count was run with other candidates eliminated in succession until the last candidate standing, who had significantly more votes than RON. Maybe someone was trying a system to see if the winner was acceptable to all voters, but it's another recipe for a mess, and when it had been arbitarily imposed with no discussion whatsoever it added to the impression that the running of ULU elections was a complete farce. In subsequent elections this impression has not dispersed.