You should still be worried its just saying that YOUR contribution will always be licenced under the curect licence. i.e they just have to release the source for the version your code was included in, which everyone would have access to anyway. BUT they dont need to provide the source code for the newer relicenced code. i.e You might contribute to version 1 then they release version 2 which is now closed source your change is still provided as source in version 1 so no need to release it for version 2. This is how I read it anyway.
Originally Posted by chenxiaolong
They real issue here and something I haven't seen anyone bring up yet is:
Whats worse for software Freedom GPL software with the CLA or code licenced under MIT. My understanding is either of them can become proprietary.