The m suffix means specifically a “pymalloc” build of Python, and it may mean that the ABI of 3.3 on your platform is not the same as the ABI of 3.3m. Extension modules must be built for the specific ABI in question. This means that 3.3 extension modules won’t work with 3.3m and vice-versa.
The change to tag Python versions was proposed and accepted as PEP-3149: ABI version tagged .so files.