thanks to binarykitten (#php on oftc) for this link.
Modern browser bugs explained in detail.
the best things in life are free.
tooltips were working for posts and mantra details except that an AJAX request was made for every url even if it had already been loaded. this wastes bandwidth and RAM and I set about making it more efficient.
the trouble I was having was that the cache was always initialized to empty. I thought at first it was a scoping problem which was not the case.