Plugins being found where they were not told to be found

[Jeff Blaine]

Our SASL build on a specific host (IMAP server) was
configured with:

   --prefix=/hostname/mail/cyrus

and

   --with-plugindir=/hostname/mail/cyrus/lib/sasl2

It has worked fine for years.

For a separate need, I built and installed a separate
Cyrus SASL 2.1.22 instance using

   --prefix=/usr/rcf

and

   --with-plugindir=/usr/rcf/lib/sasl2

The previously mentioned IMAP server began immediately
failing because it was failing to find what it wanted
because it decided to start using /usr/rcf/lib/sasl2 !!

What gives?

:(