Actually I'm not sure to understand what do you mean by "disguised colloquial form". That is was originally ما جابه , a more colloquial expression that was later on turned into ما جاء به for a literary effect? Thank you for your input!
The literary language usually choses whole expressions other than those attested in the colloquial usage - as a kind of hyper-correction, and the difference between both the idioms is not so simple..
I mean that the expression جاء به is no more than the disguised form of the colloquial جابه , as the literary language provides much more synonyms for the idea, and this occurence is very remarkable.
