Turns out that this was a mis-configuration on our end and that it works great in 1.6.0+

We had the issue on a test server that had 2 sites sharing the same IP address but moreover both sites assigned the $use_secure variable so it was being overwritten by the 2nd site and always set to 0 b/c of no match of a URI with the 1st site against the 2nd site. Resolution was simple... I just suffixed the variables appropriately for each site... e.g. $use_secure_xx and $use_secure_yy and the problem went away.

Wasted a lot of time trying to debug. Perhaps Nginx "can" be smarter and catch such a situation (i.e. that 2 or more map directives set the same variable) and perhaps issue a warning. Either way though no big deal... it just was hard to pin down... as it involved multiple file domain configs.