[cvsnt] cvs rename

[zhuyunchuan]

I did the following exp, and found some unexpected issue:
server: cvsnt 2.0.51, client: cvsnt 2.0.51
1. import a new module: access
2. cvs add makefile, cvs commit makefile
3. 'cvs log makefile' to see the history of makefile, it's OK;
4. 'cvs rename makefile makefile.txt', result was 'cvs exited with code 0'
5. 'cvs rename makefile.txt makefile', result was 'cvs exited with code 0'
6. 'cvs log makefile', result was 'cvs server: nothing known about makefile'
7. after modifying file 'makefile' and 'cvs commit makefile', result was 
"cvs server: Up-to-date check failed for makefile' "
What mistake I had made?