Myself I would go for a compromise. Flash's behaviour (using memcpy when then mean memmove) is definitely faulty, and it's not an obscure C undefined behavior either, I'm sure any C tutorial worth mentioning has "if you want to copy overlapping regions of memory, use memmove" somewhere in the middle. I'd just fill a bug on adobe's bugtracker, tell them "we'll keep the current for X months, but then we'll switch to a new implementation, so if it still breaks it's up to you". With X being a reasonable enough lapse of time.

By the way, if flash was open source it would probably be a one line patch to fix the issue, but it's not, and I wouldn't blame the fedora/glibc devs for that. Breaking things because "you can" is no good policy, but it doesn't mean you have to be backward compatible for ever, that's what being realistic is about.