It also helps if you complain to upstream for using private Qt stuff ;)
To do that I should be a bit more knowledgeable on QT/KDE.However, as an old dude, I have seen similar situation with other software an,d most of the time it was due to miscommunication:
1) Software package developers have the right to define public and private API so they do not have the burden to keep private API forever, 2) User of the software usually search for feature in the public API first but when they do not find a function they begin looking at lower level, more powerfull API 3) Software developer may be unaware of the need to expose lower level API because there is no communication on the reason developers had to use private API
So before shooting, I would suggest to ask politely whey they needed to use the private APIs and if they have good reasons put them in relation with qt dev team...
-- eric