Having just updated to 0.4.0, for both the desktop and web apps, I cannot seem to type inside CodeMirrors. I can in the pre-rendered textareas write a code block with three backticks and some text, and that text will show up in the rendered CodeMirror with a caret that I can move with the arrow keys, but I cannot add any text to it, unless I go back to the pre-rendered textarea. This happens regardless of whether the block is created empty or with a content or with a language tag.
Thanks for the reporting! A fix will be included in the next release.