AJAX Success Function using JS substr() fails in WP 4.1 vs 4.0

FWIW…
It APPEARS to have been a misconfiguration in the PHP.INI on a new Development Server (WAMP), which resulted in an unknown corruption of the code upon updating from wp4.0 to 4.1 such that PHP was injecting unwanted white space e.g. “\r\n\r\n…” in my AJAX responses (like a missing closing php ?> tag or someting?)

When running ob_clean() before returning an AJAX response, the problem went away, AND… when only the DEV copy of the project displayed the unwanted behavior, I copied the live site (wp4.1) to a mirror installation on the reconfigured DEV server, and all functions as expected.

Still, my practice of utilizing custom AJAX endpoints in future WP Projects is now officially deprecated 😉