We may naver understand this fully. Let's just be grateful, it worked thist time, and try to avoid repetitons.
If we ever again decide we should temporarily move something out of translation, it might be a good idea to remove all translate tags, so that putting it back into the system will generate a whole new set of tags. OTOH, from reading your thread, you managed to revive the content, and I think that a newly generated set of tags would lose that. Is that correct? If we can make a plan to safeguard work, we should, but if there is no sensible solution we'll just have to be careful and keep fingers crossed.
I fact, the translate tags were removed - that is why I am so puzzeled that the translation could be revived. In the Translate: page at least, I saw only the old units. I then assumed that units with numbers beyond those of the old page would be lost to translations.
Btw Yurchor thinks that we may have the same problem with other pages! See User_talk:Yurchor#The_ToolBox_page_1212.