Old Flex version in FC5?

[Benjamin Thery]

Hello,

I use Fedora Core 5 to test Mobile IPv6 on Linux.
In a recent version of the mobility daemon source code a change made 
to a lex file make the build failson FC5. This changes introduced some 
flex options to reduce warnings output during compilation.

To my surprise these options are not supported by the current flex 
version shipped with FC5. I found it strange because FC5 is very 
recent. Then, googling a bit, I discovered that flex state seems a bit 
confusing:

- Fedora ships 2.5.4a (released in 1997)
- Gentoo has 2.5.33
- Debian has two different packages flex-old (2.5.4a) and flex (2.5.33)

My question is: why does Fedora ships flex 2.5.4a and not a more 
recent one?
What are the mysteries behind flex versioning?

Thanks,

Benjamin