AUSTIN — Some straight-ticket voters have reported that voting machines recorded them selecting the candidate of another party for U.S. Senate, exposing a potential problem with the integrity of the state’s high-profile contest between U.S. Sen. Ted Cruz and Congressman Beto O’Rourke and leading good government groups to sound the alarm.

Several Democratic voters, for example, have complained the voting system indicated they were about to cast a vote for Cruz, a Republican, instead of Democrat O’Rourke as they prepared to send it. Some said they were able to get help from staff at the polling place and change their votes back to what they intended before finalizing their ballots.

Most of the 15 to 20 people who have complained to the state so far said that their straight-ticket ballot left their vote for U.S. Senate blank, according to Sam Taylor, communications director for the Secretary of State. A spokesman for the Texas Civil Rights Project said the group has received about a half dozen complaints, mostly of Democratic straight ticket voters whose ballots erroneously included a vote for Cruz, and one Republican straight ticket voter whose ballot tabulated a vote for O’Rourke.

The problem occurs on the Hart eSlate voting machine when voters turn a selection dial and hit the “enter” button simultaneously, according to the state. Eighty-two of the 254 counties in Texas have these machines, although complaints have only come from Fort Bend, Harris, McLennan, Montgomery, Tarrant and Travis counties, according to Taylor

The issue with the eSlate machine first surfaced in the 2016 presidential election. The Secretary of State’s office described it as user error at that time, and said the same of this year’s problems in an advisory sent to election workers issued this week.

“It does pop up from time to time,” said Taylor. Voters should “double and triple check and slow down” before casting their ballots, he said.

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Although the state sent the advisory, the Civil Rights Project contends that more should be done to ensure voters understand the potential for wrongly recorded votes.

The group is pushing the state to post advisories to inform voters at the polls about the problem, and how to detect it.

“This is not an isolated issue but a symptom of a wider breakdown in Texas’s election systems,” said Beth Stevens, the organization’s voting rights director. “Texas voters should have full confidence that when they use a voting machine they are indeed casting their ballot of choice.”

The Hart eSlate voting machines in Texas were last certified in 2009, meaning most of this equipment is at least that old, Taylor said. Upgrading the machines is costly: $50 million would just cover costs to upgrade machines in Harris, Dallas and Tarrant Counties, he said.

“It wouldn’t even put a dent” in the cost of upgrading machines statewide, Taylor said.

Harris County officials have echoed that the issue is a voter error and not a problem with the machines. Some voters who have tried to cast a straight ticket ballot for Republicans have also found the machine erased the vote for Cruz and records no selection for U.S. Senate.

“It reinforces how vital it is for every voter to carefully review their selections before casting the ballot to ensure it accurately reflects who you want to vote for,” read a statement from the Texas Civil Rights Project on Thursday. “Triple check your ballot before casting it.”

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Bexar County uses a different brand of voting machines, but complaints from concerned voters are still coming in amid concern for voting problems with the Hart eSlate machines, said elections administrator Jacque Callanen. When voters cast straight ticket ballots, the machines leave blank any race in which their favored party doesn’t have a candidate, she said.

“Every time we have a straight party election, we have that confusion,” said Callanen.

This is the last major election Texans will have the choice to vote straight ticket. The Legislature opted to ban the practice beginning in the 2020 election.