Easiest thing to do ia not to blame but to just find a solution and see as a team if it was a genuine mistake that is unavoidable or if you can make some adjustment to the process to ensure quality and reliability of your code.
People can specialise in a certain area of the codebase but no one 'owns' anything. Everyone needs to respect that any change to the code is a neccesary one. The 'expert' or original coder is usually a reviewer of the changes proposed anyway so thats when they can voice opinion on whether someone has misunderstood something or not.
Bugs/Features can be worked on by anyone without ego getting in the way.