In the new movie they have combiner tec.So Ithought since the twins combine to become the ice cream truck maybe they were the test subjects and it caused them brain damage. But then again maybe im crazy   and they are just stupid.  
If anyone else has any theories post them here.

 

you know, on the Live Action Movie Blog, there was a theory about the twins combining post-ice cream van. Almost every part of thier bodies are disporportionate. The bigger eye, arm, and leg could be what becomes half of thee combined robot. Skids green big eye and arm and leg form the left side of the robot while Mudflap forms the left. Since Skids is the top of the ice cream truck, his har and top lip is used, and Mudflap's chin and "beard" are used.

TF2Skidflap1.jpg (image)

^ picture. It apears that both ears are used. All info from the Live Action Movie Blog. Also his name could be Mudkid, Mudskid, Skidslap, Slapids, dik im going to stop

 

In the Transformers Movie Universe book it states that they were created from one protoform and spark which split into two (like human twins). Hence they share an alt mode to start with but they split into two bots and each is kind of the mirror image of the other in certain features. There's nothing to confirm they will combine into one robot. There is a scan of the pages from the book on here somewhere...

Voila

http://www.dorlingkindersley-uk.co.uk/static/spreads/all/4/3/9781405341134L_006.jpg

 

Um, you might want to read that scan you posted. Especially the part about combining.

 

that book is totally wrong about so much, you can safely ignore anything it says.

 

It says they can combine, forming a more substantial alt. form, not robot mode.

 

Fair enough!