Thank you both, Chunes and CalifJim!

Your answers are very helpful.
I did not know the sentence was so wrongly built.

This sentence had to mean this was Chunes has written in the correct way.

I was writing to our customer. This customer has designed a product we produce for him. According to the customer's specification we produced and sent to him the product. Then, some faults in it were detected in the customer's plant.
////I know now that a direct translation from Polish "quality fault" is wrong- thanks////
The customer could not send any complaint since the specs applied were defined by him.
Then we got corrected specifications that had to eliminate the root cause of the product's poor quality.
But, as it turned out later, the new specs also failed to solve the problem...
So it was meant like this..

Thank you once again
Jacek