The independent research, conducted for the DMA by relationship consultancy ClientView and due to be released later in the summer, also reveals that two-thirds of winning agencies have been shown losers' work post-pitch.
While 83% of agencies believe they own the copyright to their pitch work just 50% make this clear in writing.
Some agencies feel that they unnecessarily, and all too easily, negotiate away many of their rights, which can lead to lost revenue and strained relationships. This often happens when work is used across other media, overseas or when a client changes agency.
In a bid to combat these problems, the DMA will be launching a series of as yet unannounced initiatives to highlight best practice and improve the quality of engagement between clients and agencies throughout the pitch process.
Tim Dearing, who headed the ClientView insight study, said: "Most agency heads we spoke with admit they need to take more steps to protect their copyright and interests during pitches.
However, they do worry about putting themselves at a commercial disadvantage. Yet most clients do not have a problem with the agency trying to protect its work and ideas, providing the agency are not seen as being unreasonable or to heavy handed about it. Interestingly, the most lax agencies were those who expressed most concern about their pitch work being plagiarised".