Edit vs delete a running script. Why difference?

[Teika Kazura]

Hi. When you edit a running bash script, it's affected, so you
shouldn't do that [1][2]. However, I heard[3] that if you delete the
script itself from the filesystem, the original is remembered by bash,
and it continues to run as-is (as-was?). It seems correct as far as I
tried several times.

What's the, or are there any rationale for this difference? If the
entire script is read at invocation, then why should / does
modification affect? Is it a bug?

Thanks (indeed, very much) in advance.
Teika (Teika kazura)

[1]: http://stackoverflow.com/a/6303416
[2]: http://lists.gnu.org/archive/html/bug-bash/2008-02/msg00025.html
[3]: http://stackoverflow.com/a/8350089