bookmark dont work allways, why?

adobe digital editions,  version 3.0.86137

after add a pdf book to a library, and set a bookmark, often when i open it, the adobe

digital editions show the first page of the pdf book not the bookmark, othertimes

the page who the bookmark was set. why? 

when i look all pages i can find the bookmark anywhere, but how can i go directly to the bookmark?

when i read a book of 500 pages or more i cant find the bookmark again when it dont work..

thanks

daniel