Double Lane Violation

[Loudwhistle]

New one for me tonight. Free throw shooter A1 steps over the line on the first of 2 free throws. I whistle as soon as I see his foot go over the line. Of course he makes it, so it doesn't count anyway. My partner comes up to me and says I have a lane violation on B1 too! He didn't blow his whistle. I told him my violation was first and we ignore the other one. ( Actually guessed, don't know for sure) He told me later his player was standing on the block the whole time. Was this right? Thanks for the help.