All of the fenced code blocks appear on a single line in the Preview pane.

[exocom]

Note, I am running IDEA 14.0.3 on Windows 8.1 and the .md files are using LF.

This is an example block
with
3 lines

In the preview pane the LF are ignored and it outputs as a single line:

This is an example block with 3 lines

[ghost]

Code blocks never worked

```
hello world
foo bar
```

is treated like a simple text
so for me the preview is useless because I have almost in every .md code samples in code blocks

https://help.github.com/articles/markdown-basics/#multiple-lines

[nicoulaj]

Notice: This plugin is no more maintained and it has been removed from Jetbrains plugins repository. There is a Markdown plugin officially supported by Jetbrains.