There's a really picky conflict with SFC and EM, and after spending some time tracking this down, it seems to be related with how both plugins use the_content. I think I'm mainly at fault here, but maybe someone can provide some insight.
There's situation where this messes up when there's pages containing our shortcode. For example, there's a shortcode that generates a form to submit events, and errors are printed first time round only. sfc_base_meta and the wp_head stuff seems to set this off a few times to generate meta data (this is with no modules enabled) and the main page therefore has no errors.
In both cases, our page is generated more than once. The quick fix is to not delete errors until the page has loaded and all is fine, but this is highlights the fact that there's probably a lot of unnecessary processing here.
I'm thinking of adding the intensive shortcodes later on (e.g. late into wp_head?), which should help with plugins like this, but I'm worried about other conflicts that may potentially arise with other plugins.
Ideally, EM would only fire our hook once when needed, and this problem should go away, but I can't think of a straightforward way to tackle this. Any suggestions welcome!