… I think the clue here is in the 'old egg beaters' part of your question.
Check for wing waggle on your 'beaters. Over time these pedals can develop a fair bit of play in the wings, leading to wobbly shoes and accidental pulling out at inoppertune moments. Generally if you've got a bit of wing waggle PLUS some up and down movement in the cleat mechanism the pedals are the problem. I think this can be avoided by cleaning the pedals after every ride and ensuring that dirt and grease do not build up in the cleat mechanism, thereby grinding everything to bits – it needs to run totally 'dry'.
Try getting in touch with Crank Bros' UK importer (can't remember what they are called), they're very, very helpful to put it lightly. When I explained the problem with my 'beaters – I posted 'em off to them and about a week later they were returned to me with an appology, free lolly, a full free service and free new parts fitted to stop the waggling wings. Basically they were like new again.
To be honest I can't fault these guys now – and I shall be using Crank Bros stuff for the rest of my days.