Were you acting as a user who is normally able to post iframes? Note that our iframes typically get stripped unless using your plugin.
Are there some editor settings we should change? Trying to find a good compromise between allowing our authors to embed good content and keeping our site secure.
Steps:
1. Put the embed code in the visual editor
2. Hit update post – the shortcode is now gone, replaced by the actual embeddded gif
3. Switch to the text editor: the short code has now been replaced with <iframe src="//giphy.com/embed/h45algtniCWEo" width="480" height="271" frameborder="0"></iframe>
4. hit update again, the iframe is stripped because our editor strips out all iframes