NDP leadership candidate Dwain Lingenfelter responded Monday to questions about 1,100 memberships for which his campaign paid. (Stefani Langenegger/CBC)

It was an "over exuberant" volunteer campaigner for NDP leadership candidate Dwain Lingenfelter who signed up hundreds of party members without ensuring they actually wanted the memberships, Lingenfelter says.

The former deputy premier, who's considered the front-runner in the race to replace Lorne Calvert, had to do some explaining Monday as the party continued to investigate 1,100 membership applications.

The party said the Lingenfelter campaign had paid for all of the applications, some of which came from the Waterhen Lake and Flying Dust First Nations near Meadow Lake.

"The way it happens is an over exuberant sales person, one of my canvassers, one of our volunteers, in doing his job, went forward and signed up people from the band list who hadn't been interviewed," Lingenfelter said.

There was no malicious intent, he said.

"These events are a deep disappointment for me and my campaign team," Lingenfelter said.

"We have learned some hard lessons from this experience. However, the only way to guarantee that a campaign will never make a mistake is to have no campaign volunteers and to make no effort to bring new people into the New Democratic Party."

Lingenfelter said his campaign signed up 6,000 members in total. In addition to the 1,100 memberships in question, which cost about $10,000, his campaign paid for very few of the rest, he said.

The NDP does allow for someone to buy a membership for someone else, if the person who wants the membership can't afford it.

However, under the rules, the member has to sign the membership. In this case, the volunteer signed the memberships.

Membership drives and leadership votes tend to go hand in hand, because members are allowed to vote for the candidates they support.

Lingenfelter is one of four candidates running for leader. The others are Deb Higgins, Ryan Meili and Yens Pedersen.

The party selects a new leader on June 6.

Meanwhile, in the legislature, the Saskatchewan Party was crowing about the controversy.

Saskatchewan Party MLA Dustin Duncan said although Lingenfelter apparently didn't have any money to donate to the NDP last year, he had thousands to buy memberships.

"The NDP is trying to downplay the phoney membership scandal," Duncan said.