This seems to happen most at Flickr, bit when trying to select several lines of text, if the top or bottom line is a lot shorter than the middle lines, the highlighting function seems to acquire a mind of its own.
It seems to either prefer a rectangle that does not include the full lines in the middle, or wants to select the whole column on the page. Many groups have award text they want you to copy when commenting on images. It is darn near impossible in some groups to do it on the ipad. (iOS 4.3 though it seems to have happened in all the releases). Anyone have a solution?