A recent file-system bug has been found with EXT4 that has made its way into the stable Linux kernel releases 3.4, 3.5 and 3.6. This EXT4 bug results in data-corruption and it is activated when the file-system is unmounted too frequently within a short period. It might also be triggered by frequent reboots, although the practical chances of that happening are relatively low.
The user reporting the bug writes,
The bug did really quite a lot of damage to my /home fs in only a few minutes of uptime, given how few files I wrote to it. What it could have done to a more conventional distro install with everything including /home on one file system, I shudder to think.
A detailed explanation of the issue is present in this LKML mail. It says that the trouble started with an EXT4 patch made in Kernel 3.6.2, which was later backported to Kernel 3.5 and 3.4 as well, spreading the problem further and further behind. There is no fix for this issue currently, and developers are working on a fix for the latest stable Linux kernel.
Here is the beauty of open source software development. A bug is found, and because the source is open for everyone to see and modify, people jump in to solve it as a community effort. Soon thereafter, a solution is found and the issue is fixed. This is unlike closed source programs, where you have to wait for the organization controlling the code to step up, modify the code and keep updating people about what it is doing. Moreover, in the world of closed software, you would not even know what went wrong to begin with, unless someone digs it up.