I’m using the PHP Markdown Extra plugin on several Multiple Site Manager sites, and after I upgraded to EE 1.6.5/1.6.6 I get a blank screen when I add or edit entries in the control panel, and I get blank screens when I go to a single-entry template.

I think the problem is caused by the the Typography updates in 1.6.5 described here and here. Is there a fix for the PHP Markdown Extra plugin? We have hundreds of entries formatted with Markdown and it would be a major effort to reformat them.

Is it this Markdown plugin that you’re using?  I don’t believe there should be an issue with it- unless another extension is interfering.  Do you have any others installed?  I believe ‘File’ was one that had some issue with the typography change.