Some early voters in Texas have said that voting machines flipped their selections when they tried to vote straight-ticket, including in the state's high-profile Senate race, the secretary of state's office said Friday.

Voters reported issues with Hart eSlate machines, which are used in about 30 percent of Texas counties, according to the Associated Press . People from both major political parties have reportedly complained that when they make a selection designed to let them choose all candidates from a given party at once, the machines in some cases have chosen a candidate from another party. The secretary of state's office, however, said the mishaps were due to user error.

"The Hart eSlate machines are not malfunctioning, the problems being reported are a result of user error – usually voters hitting a button or using the selection wheel before the screen is finished rendering," Sam Taylor, spokesman for the secretary of state's office, told the AP.

The Hart eSlate machines don't provide voting receipts and are used in about 80 counties, including those that encompass Houston, Austin and Fort Worth.

The AP reports that in an advisory to county clerks and elections administrators Tuesday, Keith Ingram, the secretary of state's office's director of elections said, "We have heard from a number of people voting on Hart eSlate machines that when they voted straight ticket, it appeared to them that the machine had changed one or more of their selections to a candidate from a different party."

An election administration in Fort Bend County told the Houston ABC affiliate, KTRK-TV, that he had reported the issue to the secretary of state's office years ago but hadn't seen a remedy.

The state's Democratic Party accused the secretary of state's office of not doing enough to warn voters and called for a statewide announcement and better training for poll workers.