Ubuntu 15.04 crashes or freezes when I select text by dragging with the mouse in LibreOffice Writer. It also occurs to me when I click on the menu to select it.
The only solution is to turn the PC off and on via the power button, because the cursor does nothing.
Well I know this may not be an answer you want to hear, but since your not using an Ubuntu LTS version, all you can do is send a bug report. Sadly there is no other way I or a lot of other people can help you. If you are in a work intensive environment, or want a stable OS. You should install the current LTS version of Ubuntu, or its flavors.
15.04 and any non-lts release will not only be lacking in support from Canonical and the Ubuntu devs, but non-lts versions are susceptible to bugs that may not be "fixed On a dime." Just because you have the latest version of the Ubuntu, does not mean it is the best. Mainly because most non-lts versions are used as a testing ground for features. These features are not yet 100% bug tested, but are planned to be in the next LTS release, or milestone release.
So if your looking for a stable OS use the latest LTS. Below I posted Links to the ISO's for the current LTS versions of the Ubuntu flavors for 14.04. At least the most popular. I don't think your using Kylin or Mate.
Sorry I could not help in any other way :'(
