Thank-you for your answer. I forgot a little thing to write about my issue. These 2 block are part of a tab page ( I have several tabs on my canvas).
Therefor, my canvas is a Tab Canvas type.
Anyway, I managed to solve this problem. I realize that it is possible to merge an item to a block, although the whole block (all the item in it) is base on database tables, and the attachment item is non-database depended.
thus, I have only one data block and I don't have a problem of scrolling any more...
Thanks again for your answer!!! ( The only one who answered to me....)