The Secretary of State is alerting voters that some voters who changed their party affiliation in the last few days may get two ballots. But only the second one will be counted.
From a statement:
Late Party Changers May Get Two Ballots
Voters should only cast the ballot that reflects their current party affiliation
(Salem, OR) Due to the extraordinarily high number of Oregon voters who've recently changed their political party affiliation, there will likely be a number of voters who will receive two ballots for the May 20 primary.
This affects only those voters who've changed their party registration (from one party to another, or from non-affiliated to a party) in the last week to two weeks. When ballots are mailed May 2, some voters will first receive a ballot with their previous registration. These ballots should not be voted.
Instead, affected voters should wait until their new, updated ballot arrives, and then vote only that ballot. The outdated, incorrect ballots should then be destroyed. This situation will not affect voters who have registered for the first time, only those who've recently reregistered with a different party.
Note: Even if two ballots are cast by the same voter, only one ballot--the updated one with the new party affiliation--will be counted.
More details on the jump...
What caused this scenario? In order to prepare and mail out more than 2 million ballots on time, county elections offices begin preparing their ballots up to two weeks in advance of the mailing date. If a voter changed their registration after that date, they'll receive the one that has already been prepared for them, followed by a new ballot reflecting their party change. This happens in every election, but it's never before impacted so many voters.
How many people are affected? It varies from county to county, depending on when county officials started preparing their ballots, but the statewide number will be in the thousands. Note: Numerous counties have been able to pull some or all of their affected ballots.
What happens if a voter casts the ballot that has their old registration? The state's centralized database will catch the error automatically (the ballot envelope bar code contains the voter's ID and ballot style), and that ballot will not be processed. Instead, it will be set aside until all other ballots are processed. If the second, updated ballot is cast, only that one will be counted, and the old one will not be counted. If the voter sends in only the out-of-date ballot, only their votes in non-partisan contests will be counted. Again, under any circumstance, only one ballot will be counted per voter.
For reference, this process is laid out in the Vote By Mail Procedures Manual, which can be found on the Oregon Elections Division's website.