Student or Learner
I need your help with this sentence:
"The European plasticiser market was again tumultuous this week as prices climbed higher and buyers warned of retribution when supplies lengthened".
In my opinion, there is a mistake in this sentence. It should be "lengthen" instead of "lengthened", am I right?
However, if they buyers started to warn that retribution would happen in the future, when supplies start to lengthen, then they should have left it without "ed".