shortcode params no longe parsed?

Hi,
We’ve been using your excellent plugin for a while.
At some point in the last few months (hard to say apologies!) the parsing of shortcode params no longer seems to be working. We are on the latest version of the plugin. Specifically the allowfullscreen param
e.g.
[iframe allowfullscreen][/iframe]

We would expect to render:
<iframe allowfullscreen=”allowfullscreen”>
But instead we get
<iframe 0=”allowfullscreen”>

I’ve removed the other classes / url for simplicity.

Any ideas?
Thanks in advance!

Alex