Mistakes were made...

... an admission of someone else's guilt?

'Mistakes were made' - this is used when someone flags a developmental code error or coding shortfall where the guilty party is not known (at the time*).

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Even wiki has an entry although I don't think attributed to me! Read "Mistakes were made on wikipedia"

* Guilt is not known at the time but SVN/GIT can lead to blame someone but this is usually not mentioned to save all parties. It could always come back to bite you some other time.