That's how they grow.

In their natural environment they grow along the ground with only the top end aiming upwards. They may branch out and grow new roots along the stem but mostly they just snake along the ground.

I posted about this question last year on the IAS aroid forum and that seemed to be the consensus among the expert aroid growers.

Here is a link that might be useful: Dieffenbachia growth pattern

thanks for the information and the link, atleast now I know it's not something I am doing!

Yeah, that's what I thought too. For several years the thing flopped around and needed to lean against something or be tied up. I de-potted it a couple of times to check the roots but they were always ok. The stem was firm like a hose under pressure and no mushy spots but it would bend so much it could be potted up but bent over and running along the floor. Now it's bound to a pole and almost touches the ceiling, I guess I'll have to give it the chop one of these days.