Hey, nope it's not normal.
Can you please detail the exact commands you wrote when you dumped the boot.img?
While for the second problem, your command is not correct, you missed "flash". It's
Code:
fastboot flash boot_a yourpatchedimage.img
boot_a or boot_b of course depending on your active slot.
And don't flash your big boot.img file. It should be around 100Mo only.