[helibird]

I use a Kobo Aura H20. It has e pubs bought from kobo, some direct from authors and some brought from amazon and converted to epub using calibre.
Occasionally I come across a book that always opens on the first page. I usually open the contents page and click the nearest chapter that i remember and scroll the rest of the way. Clicking the chapter puts a tick by that chapter but the next time I open the book the tick as gone back to the first chapter. I tried bookmarking the page but nothing shows up in annotations.
As it is only on a few books by the time I get round to investigating I've forgotten which ones so not sure if they are converted or not!
I am fairly sure it is a book problem not a Kobo problem as it only occurs occasionally.
Anyone got any idea what causes this and is there an easy way to fix in Calibre (I don't currently touch any of the conversion options on Mobi files just go with the default)
I'll try and remember to note down the book next time it happens.
Thanks