Wistia's embed codes are designed to be very durable, but WordPress has a
history of being particularly troublesome. This plugin adds oEmbed support so
that pasting a link to the video's page in Wistia will embed the video. The
video's URL must be by itself on its own line for this to work.
As of version 0.6 of this plugin, it is recommended that you check
"Use oEmbed?" under Advanced Options when generating your embed code.
As of version 0.8 of this plugin, the legacy "Anti-Mangler" feature is an
option that is turned off by default.
See the Wistia documentation for more:
http://wistia.com/doc/wordpress#using_the_oembed_embed_code