Hi Pascal,
As you know, o1p_o2p is a tiny utility program to check if O1P and O2P atoms of a phosphate group are labelled properly. The program is as useful as before, so still distributed as part of 3DNA v2.1. In my experience, whenever I check a feature consistently throughout nucleic acid containing structures in wwPDB, I (nearly) always find some inconsistency. As a test, you may run o1p_o2p on all entries of the current NDB, and see what you get.
I am sure you are aware that O1P/O2P have been labelled OP1/OP2 respectively as of PDB format v3. The o1p_o2p program recognizes the new naming convention internally, and the output can be written accordingly with option -pdbv3.
In the v2.x series, I've been trying to keep 3DNA backward compatible, with added features/programs and improved functionality for each new release. It is imaginable that in 3DNA v3.x (in the not-too-distant future), among other things, I will reorganize/consolidate program structure, unify command-line options and configuration file formats. At that time, I am sure o1p_o2p as a stand-alone program will be gone, but its functionality would be integrated into a more versatile program.
HTH,
Xiang-Jun