Tens of thousands of Californians have been registered to vote incorrectly by the state Department of Motor Vehicles, including some who were assigned the wrong political party preference, officials said Wednesday.

Officials insist the errors were limited to 23,000 of the 1.4 million voter registration files sent to elections offices between late April, when California’s new automated “motor voter” system went into effect, and early August. Californians who were affected will soon receive notifications in the mail instructing them to check their voter registration status….

The errors, which were discovered more than a month ago, happened when DMV employees did not clear their computer screens between customer appointments. That caused some voter information from the previous appointment, such as language preference or a request to vote by mail, to be “inadvertently merged” into the file of the next customer, Shiomoto and Tong wrote. The incorrect registration form was then sent to state elections officials, who used it to update California’s voter registration database.

A small number of the mistakes — officials estimated around 1,600 — involved people who did not intend to register to vote. State officials said no people in the country illegally — who are eligible to get a special driver’s license in California — were mistakenly registered to vote. An unknown number of errors included voters whose political party preferences were changed without their consent. Officials did not provide additional details about the errors they uncovered during a monthlong investigation.