I have never had a sheet of film "jump" out of the grooves in a Combi-Plan, but I always use the red film retaining clip, and push it down just enough to engage the films firmly. I also use the technique of pre-filling the tank with developer, and then putting the film rack into the tank in the dark, then putting on the lid, turning on the light to time and agitate, turn off the light dump developer, pour in stop, put lid on, agitate, pour out, put fixer in, put on lid, turn on light and fix, then remove lid with light on to pour out fix., and I affix a hose to the bottom spigot to wash, where the water rises up inside the tank and spills over the top for the flow.