Payload names in two ways to send a file

I observed this behaviour in two ways to send a file:

1) File "EDIFILE 123 ABC.txt", sent via "send file to partner" window

- Payload name as displayed in the sending AS2 system: "EDIFILE 123 ABC.txt"
- according to tab "raw data (unencrypted)" in message details: Content-Disposition: attachment; filename=EDIFILE_123_ABC.txt
- Payload name as displayed in the receiving AS2 system: "EDIFILE_123_ABC.txt"

2) File "EDIFILE 123 ABC.txt", sent via outbox directory

- Payload name as displayed in the sending AS2 system: "EDIFILE_123_ABC.txt"
- according to tab "raw data (unencrypted)" in message details: Content-Disposition: attachment; filename=EDIFILE_123_ABC.txt
- Payload name as displayed in the receiving AS2 system: "EDIFILE_123_ABC.txt"

This brought up the following thoughts and questions:

a) Is it really intended (and necessary) to have the locally displayed payload names treated differently for those two ways ?
I think, the way to send the file shouldn't make a difference.

b) Is it necessary for the sending AS2 system to replace spaces by underscore ?
I would expect that - if at all - only the receiving system should perform this kind of replacement ... e.g. if necessary due to OS restrictions.

c) If the replacement (spaces to underscores) is a must for the sender, I would expect that the sender displays the payload name in the same way as it is transferred to the receiver according to field "filename".
(e.g. always "EDIFILE_123_ABC.txt")
What do you think ?

My testing environment:
Sending system: Host A, mendelson AS2 opensource build 55
Receiving system: Host B, mendelson AS2 opensource build 55

Foren
AS2