Geshi and full html issue

When editing a page in full html mode with this procedure:

1 switch to source code
2 add code in a get block in
3 switch to full view

the code is loosing all its lining. It goes form:
from ROOT import std
v = std.vector(int)()
for i in range(0,10):
v.push_back(i)

to

from ROOT import std v = std.vector(int)() for i in range(0,10): v.push_back(i)

I have a Drupal 7 website and my filters on full HTML are:
GeSHi filter*
Convert URLs into links
Correct faulty and chopped off HTML

Please inform me if I have missed any important information.