mexport does not separate mails with blank lines

[skarnet]

Hello, I'm trying to concatenate several files, containing one mail each, into a single mbox. What I'm running:

echo file1 file2 | mexport > mbox

What I'm expecting in the mbox file:

From sender1
Headers1

Body1

From sender2
Headers2

Body2

What I'm getting:

From sender1
Headers1

Body1
From sender2
Headers2

Body2

Is this expected?