I read the book for the first time only recently, and while there were several things about it that I loved, and even more that I could love for my child-self, even if current-me was more detached, that memory wiping really bugged me.

I mind it significantly less in Seaward both because it seems to fit more organically with that book's sense of a dream out of time and because it is explicitly promised not to be forever: they will remember when they meet again. It seems wholly artificial in Silver on the Tree.