IMHO (and this will probably start another debate!), DE filters should be broken down and cleaned, not backwashed. My reasons are as follows:
1. when you back wash you really don't know how much DE has washed out so you really don't know how much DE to replace...too little and you will not have good filtraton...too much and you might get bridging between the grids (and if you have ever had to pick away at rock hard DE stuck between the grids you understand what I mean!)
2. Backwashing forces water backwards through the grids....If you run a DE filter without DE, even for a short time, you run the risk of dirt clogging the grids and the grids getting coated with oils and organics. You then have to break the filter down and clean the grids...when you backwash you are still forcing dirty water through the grids (backwards) and the same thing can occur.

As far as "bumping' a DE filter....knocking the DE off the grids so the dirt can mix with it and then recoating the grids is not a good idea, IMHO. Dirty DE is dirty DE!

Just my 2 cents!