I am using Linux Mint 13 Maya Cinnamon 64-bit. My Vim version is 7.3 and I installed the latest version of Janus.
I found that for any files with a hash "#" in its content, the syntax highlight for the file does not work. For example,
# test
print "Hello"
The 'print' has color while I am editing the file. But when I save it and open it again the whole file loses syntax highlight.
If I deleted the first line and save, the syntax highlight comes back after I open it again.
This applies to all kinds of files such as .py, .c and .h. If there is a hash "#" character in the file, syntax highlighting does not work.
I have already tried "syntax on" but nothing changes.
I don't know Janus so this answer might not be 100% useful for you, but let's see. You could try finding out where the settings have been set. Try this:
Get current settings:
:set filetype? syntax?
Check where these have been set:
:verbose set filetype? syntax?
Execute these commands when you lost your syntax highlighting:
:syntax on
:set ft=python
:verbose set ft? syn?
Here you should see which script changed your filetype after saving. Normally, vim uses heuristics to determine the correct filetype if the file extension is ambiguous. In cases where these heuristics don't work, you usually set a global variable in your vimrc to a fixed value. In your case this would be something like:
let g:filetype_py="python"