I would imagine that if you submit code to an open source project and leave the license as it is, then you release that code under the license. The only way it wouldn't be is if someone other than the owner/copyright holder submitted patented code.
For example, I could try to submit a pull request to an audio/video project to add an H.264 decoder/encoder that I wrote myself. That is OK because I wrote the code, and therefor I own the copyright to that code.
However, anyone who tries to use this code can be sued by MPEG LA for money or they can even ask them to cease and desist outright if they wish -- because it's their patented technology! It also works the other way around, if I wrote both the code and acquired a patent for the technology.
A CLA is the only way to stay safe, as far as I understand, but most open source projects just don't use them (except very large ones, like the Linux kernel etc).
It also mentions that there is an 'implicit' patent grant provided by the revised BSD license[1] but that it has never been tested in court (which I presume means it is not advised).
I guess Apache 2.0 (or if you're a copyleft kind of guy, GPL3) is the way to go!
[1] http://en.swpat.org/wiki/Patent_clauses_in_software_licences...
Uhh ... The Linux kernel doesn't use a CLA. It uses Developer Certificates of Origin: the Signed-off-by lines.