Blank pages on some pdf read with M92
I have noticed that within the pdf reader some few pages of some ebooks are surprisingly not displayed at all with my M92, while few others are partially displayed. If I turn pages forwards or backwards, the page counter increases, but the screen keeps on showing blank pages until a dozen pages thereafter I can see the text. The direct goto page command also points to the blank one or even, wrongly, elsewhere.
I also noticed that this occurs after some reading sessions. In some respects, it seems that the pdf "deteriorates" with time. The only way I have been finding in fixing the trouble, is replacing the book in the reader with a fresh copy from my PC. Besides being quite annoying, so done I am also afraid I lose all the important annotations collected in between. Is there some way to workaround this problem or at least to replace an ebook without losing the precious glyphs?
I have updated the firmware to last decade of april, 2013 with no result at this respect.
Thanks so much for the attention