By verify I mean having the Verify option enabled in ImgBurn: it cycles the tray to ensure the disc can be properly identified after removal and then checks data on the disc against the source image/files. This tells you if the disc is fully readable or not.
Active OPC is part of the burner's strategy for writing the disc with the highest possible quality, so it can't be turned off, and even if you could, you would then get lower quality burns and very possibly unreadable discs.
Your other Pioneer burners also perform active OPC, but maybe in a less frequent way, and that could be why you didn't notice before. Newer burners tend to do a lot of OPC "stop and check" operations, especially when burning at faster speeds.
You can check all of this by looking at the burn graphs (in ImgBurn go to Help -> ImgBurn Graph Data) and also by looking at the myce/cdreaks forums.