No. Just no. This is like saying, "well, this particular case of a use after free worked before, so changing the implementation of malloc to break this program without warning is irresponsible." No. It's not. There is a clear delineation of responsibilities. That delineation is documented in the relevant standards. That delineation says that if you use memcpy with overlapping regions, you are doing it wrong. This has been the case SINCE THE DAWN OF C. Anyone using memcpy with overlapping regions wrote a buggy program. Anyone whose program is broken now has to fix it. Their programs are buggy; they need to fix the problem.
If you don't hold people accountable, you encourage bad behavior. I'm glad glibc has a maintainer willing to hold people accountable for their bugs.
That being said, if Fedora wants to roll back to the old version until the bug is fixed, that is their business, but I wouldn't recommend holding every other program back for Adobe Flash. Just ship a workaround library for Flash and be done with it.