From this discussion: https://groups.google.com/d/topic/liftweb/K14YPMlWNyY/discussion
I see what the issue is. SHtml.memoize is using the second stack frame as it's salt assuming that is the caller. Since SHtml is a singleton object though, there seems to be an extra frame involved. The stack trace looks like this.
I'll update it to use the following frame and submit on review board.