Some horses have a different sort of gait that helps them through the mud,,,Usually a higher striding type ..thats why some are bred to run through it like Palace music , Woodmans , Easy rockings offspring ect ..

I remember watching a horse called Cent per Cent race in a trial and noticed his action,,,his first start was on a slow and he just bolted in,,also won a another,,,i backed him again when up here in Brissie on a good track and he he didnt know what to do,,sort of jumping up and down on the spot,,,hes more educated now and has performed on the dry since..

Alot of horses just dont have the confidence to stride out (let down) as they feel like they are skating..its seems really hard or impossible to train the horse to run through it,,they either are bred to run in it (gait) or have no hangups about the shifty ground.

Rememer though a heavy at some tracks can be a different to other tracks even if the peno is the same,,Something to do with soil types and drainage ect..

Hope i've helped or i could have just confused you more