Yes I've seen it, but it wasn't my situation there was a post on here I responded to and the owner happened to be local to me so I met her and the joeys and made a team to help her try to hand raise the joey... The original post is here http://www.sugarglider.com/glidergossip/topic.asp?TOPIC_ID=60693&whichpage=1
I don't know that I would call it "miniature gliders" or even "dwarfism", I would describe it as "failure to thrive" as the owner did on her post. I also feel that the mother knows the joey isn't thriving and or senses something is off with the joey and that's why she rejected it.
These joeys are the same age born at the same time. Gram was very well taken care of but despite all the owners efforts he passed away. His brother is thriving and doing well. Gram struggled to gain weight and keep it if he did gain, he teetered on 10 and 11 grams for a few days but did seem to start gaining for a week or two before he passed.
I'm sure the owner would be happy to talk to you about him if you would like more information let me know n I'll get you two hooked up