In the Jordanville Prayer book, for the translation of Ps. 50, we see something like this:
"Against Thee only have I sinned, and done this evil in Thy sight, that Thou mayest be justified in Thy words, and prevail when Thou art judged." - (Ps. 50)
I must admit that I have never understood the last part. This makes judgment day sound like we and God are judging each other, or that it will be some type of contest. What exactly is this talking about? Is it just implying that our works will be compared with the Father's perfection, as that is to be our goal? In what way can we say that the Father "is judged"?
Other translations seem to make things clearer and be saying something different, like the KJV:
"Against thee, thee only, have I sinned, and done this evil in thy sight: that thou mightest be justified when thou speakest, and be clear when thou judgest."
Is this because of a difference between the LXX and the Hebrew MSS? This does perhaps seem to be the case from the LXX translation I looked at, but it still wouldn't provide a reason for the change, or what the new language meant theologically.