Ver: 1.5.2 - Connection Error: Failed to reach the server - Compose new window

[cerrmj]

When using "Compose in new window" option if the new window is open too long and you hit "Save" or "Send"  the error "Connection Error: Failed to reach the server" pops up and one can't send or save the message to drafts anymore. 

The use case here is one begins composing a message in a new window - then gets called away for maybe as long as an hour or two and wants to pick up where you left off in composing the message.  The window allows you to continue typing in more text and finish your message - but when you hit send or save you get the "Connection Error:" and any changes you made after you returned to the message are lost. 

I tried toggling the "Save in browser's local storage (temporarily)" setting on and off and it has no impact on the "Connection Error:" in this scenario.  I also tried using Chrome and Firefox - both have the same behavior.

Is there a timeout setting somewhere controlling this?  Is there anyway to leave the "Compose in new windows" open for as long as one needs to finish the message?

Thanks in advance.
Bob.

[Dmitry42]

I think this can be session timeout (by default 5 min).
As I remember in RC config you can change this option.

[cerrmj]

I found and updated the following setting $config['session_lifetime'] = 180 in the config.inc.php and that didn't make any difference.  Any other ideas or is maybe this something related to an imap timeout or something?