If this is a 'Surprise!' to any coders, they're still living in the 20th Century
This core FAILure of Object-Oriented coding has been blatant and well known for decades. O-O turned into Uh Oh!
If you pull code you didn't write from anywhere and stuff it in with your own, expect problems. That's the lesson of Object-Oriented coding. And of course, there is the usual litany of why this is the case:
1) Inadequate Coding Tools and languages.
2) Code-By-Committee, which is the default these days for mammoth projects, with consequential incoherence.
3) Code complexity beyond the comprehension of any single human.
4) Poor or no code documentation. This is commonly for the sake of the usual short term thinking of profit over code quality.
5) Lack of adequate code QA.
6) Lack of vetting of incoming foreign or internal code objects. IOW blind faith.
7) . . . Add your own . . .