[Users] Can user trigger sending same mail twice at once ?

[Michael]

I just see the same mail sent twice in my sent folder. It had a massive attachment.

I was working ahead while sending so i'm not sure what happened, but think i did this: 

Sending the mail just from the compose window, and while it was uploading, went ahead editing another one (also with big attachment) which i put into the queue folder by the respective button (<put into 'queue' without actually sending>). 
I wanted to wait for the first upload to finish and then send the next.

However, being distracted, i clicked the <send all mails in queue folder> button before the first mail finished. I expected the second mail to start sending in parallel.

However, what happened was, the first mail (still being in the queue folder) got sent a second time (and in parallel to the unfinished first version) and only after that, the second mail started launching.

I'm not sure if that really happened, as i said i was distracted and i'm also very late. 
Just my question, can it be claws have a feature here and it was simply correct to send the same mail twice ? 
But shouldn't there be a sanity check somehow against sending a mail again which already is uploading ?
Or am i mislead somehow and it wasn't really possible (so something different happened).