Do block device changes propgate to mounts

I've been using debugfs to write/change block devices directly, and I'm seeing inconsistencies when it comes to existing mounts of that block device, the changes I make don't always appear in the mount.

When do changes to the block device propagate to existing mount points of that device?
If the mount is read-only - does that have any effect?

For example:
Code:$ debugfs -w /dev/rootfs_device
(debugfs) cd lib64
(debugfs) write my_library.so library.so
(debugfs) close -a
$ ls -al /lib64 # Changes don't always propagate to mount (maybe there's a correlation to file size?)Thanks