In the index we have

~, see destructor

followed, after a few lines, with

~, see operator, ones’ complement

in contrast to other things (e.g., &) which have one entry with multiple _see_s.

Looking at the source, we have \indextext{~@\tcode{\tilde}|see{operator, ones'~complement}} in [expr] and \indextext{\~@\tcode{\tilde}|see{destructor}} in [special] (with an extra backslash before the first ~). I don't know enough LaTeX to know which one is right.