Non-Monotonicity in Australian Preference Voting
There are several methods of voting which allow voters to rank candidates in order of their preference, rather than just selecting a single desired candidate and then doing a single count (Plurality or “First Past the Post” voting). The system specifically used in Australian elections is “Instant-Runoff Voting” (IRV).
IRV is intended to allow for a variety of political parties of various sizes to flourish (unlike the famously two-party-dominated politics of the USA) as citizens who vote for a minor party as their first preference don’t “waste” their vote; if their first preference is too obscure to get in, their vote goes to their second preference, and so on.
However, it is still possible for “vote-splitting” to have a negative effect on minor parties - in some cases, giving a candidate a higher preference can paradoxically cause them to lose, as they can be eliminated earlier.