Comment 1 for bug 575542

This is a true statement. Getting this right will require kernel support as well as changes to e2fsprogs, since the kernel ioctl used by online resize currently assumes that the blocks used for the allocation bitmaps, et. al, are in the block group which is added.

This shortcoming isn't really user-visible, although it will cause barely noticeable performance differences for resized filesystems versus file systems that were originally created at that size. It will also impact fsck time somewhat. It's a known problem, but it's relatively low priority to fix.