exiting chroot leads to getpt failure

On a Debian Jessie machine I have a rootfs image which I chroot in this way:

mount myimage.img /mnt/myimage
cp /usr/bin/qemu-arm-static /mnt/myimage/usr/bin/
mount --rbind /dev /mnt/myimage/dev
mount -t proc none /mnt/myimage/proc
mount -o bind /sys /myimage/sys
chroot /mnt/myimage

on exiting I do the opposite:

rm /mnt/myimage/usr/bin/qemu-arm-static
umount /mnt/myimage/sys
umount /mnt/myimage/proc
umount /mnt/myimage/dev
umount -l /mnt/myimage

But when I try to open a new terminal in my host machine I get the following error:

Execution of the child process failed

getpt failed: file or directory not exists (translated from Italian)

Perhaps I'm forgetting something?

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