I have created few site columns and created site content type from that columns and attached it to my SharePoint list.
Now when I was trying to access some column via object model code its was giving me an error saying that column doesn't exists.
By looking at the column internal name I found that the first character of column name was replaced with some hexadecimal code. :(
Spending some hours on that I found that SharePoint requires first 4 characters of the internale name have to be non numeric.
Creating column with first four characters as non numeric resolves the issue.