以前一直遇到这个问题，偶尔遇到。这次升级到14.04后，必现了，每次重启系统都不行，都要用CCSM重新设置一次才行：

网上已经有用户反馈过这个bug： https://bugs.launchpad.net/ubuntu/+source/compiz/+bug/858845

After yesterday's update it seems to be "fixed". Yay!

Still need the following workaround:
Open ccsm, go to Preferences and disable auto-sorting.
Expo has to be at the bottom of the plugin list for hot corner to be remembered.
Then followed by (in ascending order, i.e going up the list) scaleaddon, unity shell and scale so hot corner for spread (scale) would work too.
Basically the same work around in 13.10 but the order wasn't as stringent before.
In particular hot corner for expo used to work without being near the bottom of the plugin list.

Haven't brought in edge flip for wall, I just set the unity launcher to auto-hide this time.
Not sure if edge flip will work (used to have to place wall at the bottom, but the spot is now taken by expo, if put it in second place scale get pumped up so that may not work)

It is not really a fix but at least the work around from before sort of works. I am relief.

解决办法为，打开 CCSM，首选项中，禁用自动排序，然后把expo放到最下面。

下次重启好就了～～