The story behind that is,... just coding life.
Someone from the team developed for the customplugins are faster method to use them. This pattern used static calls. Then we used that pattern and were quite happy, but it was nasty to write for it, because it was not used as true object.
During the optimisation phase we found out how to use the standard or better enhanced joomla plugin pattern and to boost the whole thing with a little trick. But this little trick didnt worked for the customs. So we were forced to rewrite all triggers of these family and this is causing us so much trouble. But now we have the possibility to write more powerful plugins then before. So it will come back, you can be sure.