There is definitely something wrong with the actual Python 2.5 implementation.
It seems that there are different implementations used on different servers.
Please have a look at my submissions 5357523 and 5357524. The code I submitted is exactly the same, but runtime and memory usage differ significantly. Standard runtime for a Python program that does nothing more than starting the interpreter used to be 0.03 s for Python 2.5 and memory usage used to be 3.7 MB. This is congruent to my submission 5357523. But submission 5357524 takes 0.18 s and 4.4 MB for exactly the same code.
Same problem with Python 3 installation. Two submissions of the same code:
Submission 5357623: AC in 0.91 s with 5.6 MB mem
Submission 5357624: AC in 2.64 s with 6.6 MB mem
Another one: The Python 3.x installation lacks the random module. See my submissions
5357566 (AC) and 5357567 (NZEC) - same code, but random module imported (and not used!).