Hi François;
That is hard to say as OCX's are 3rd party controls where each one can have its own vendor nuances. It could be an issue between PB its hand-shake to the OCX. In that case, it could be fixed within the PB run-time. However, if the issue is within the OCX itself, then the source vendor could be the place to get the fix.
I have not personally noticed any fixes from PB 12.5.1 through 12.6 build 4091 that addresses anything OCX specific. However, I'm not sure if I missed an EBF that addressed this area. Sometimes, an unrelated EBF can correct another aread of PB (or break it). So it might be possible that some fix in anther release may have cleared your problem.
Have you tried the approach that Prajeesh used in his workaround?
Regards ... Chris