Postman SMTP on "[Plugin: WordPress MU Domain Mapping] Redirecting to wrong site"

If the request isn't going to your multisite install then the issue is either with your DNS or your web server configuration.

The request is definitely going to the multisite install. The only place the mapped domain knows about the subsite is through the WPMU Domain Mapping configuration.

The original site domain: http://wordpress-hendriks.rhcloud.com <- works 100%
The subsite: http://wordpress-hendriks.rhcloud.com/programmer <- redirects to root :(
And the mapped site: http://www.codingmonkey.ca/ <- works, but buggy behaviour

Here's the 'mapped' domain CNAME:

www.codingmonkey.ca.	IN	CNAME	ec2-54-82-146-173.compute-1.amazonaws.com.

And the DIG A results for the original domain:

wordpress-hendriks.rhcloud.com.	47 IN	CNAME	ex-std-node225.prod.rhcloud.com.
ex-std-node225.prod.rhcloud.com. 59 IN	CNAME	ec2-54-82-146-173.compute-1.amazonaws.com.
ec2-54-82-146-173.compute-1.amazonaws.com. 21599 IN A 54.82.146.173

Clicking codingmonkey.ca shows the WordPress subsite, and that's the result of the Domain Mapping plugin.

It's possible that your web server wasn't restarted after you made your configuration changes. Do you have the option to restart your web server?

I do. In fact every time I deploy the PHP files with GIT, OpenShift automatically restarts both MySql and Apache.