Same here, happened twice when browsing the store in 10 minutes. Arch with kde4.
I frequently have this issue too. When it happens, try right clicking, then click somewhere else to remove the context menu. Arch with xfce4, catalyst drivers.
Confirmed here, but only happening when I use Steam Community. I'm using Plasma 5 on Kubuntu 15.04. Minimizing and restoring the app or using show desktop global shortcut fixes it temporarily, until I click on a link in the community section of the client again. It's not intermittent for me. It always happens when using Steam Community.
I am experiencing this problem as well. Frequently, Steam seems to steal the mouse and ignore clicks. Doing 'killall steamwebhelper' from the terminal does not help, so I suspect it is Steam proper rather than the webhelper. I am running Linux Mint 17.2 x64 with the Cinnamon WM. I should also note, though I am not sure if this is just regular behavior, that I have to use kill -9 to kill the base steam process. Steam does not respond to a more polite kill request.
The same thing just happened to me. I'm running GNOME shell on Debian with proprietary Nvidia drivers. I've had Steam on this computer since about the time it was released for Linux, and this so far is the only time it happened. I, just like otakucode, tried to killall both "steam" and "steamwebhelper", but had no results until I did kill -9 on "steam.sh".
I encountered the same problem once I press the middle mouse (usually when I intend to smooth-scroll). In such case I can get the function back by pressing right mouse button to open the usual action menu.
Cause of the Problem:
I tested the same thing with CTRL+C (copy) and it causes the same problem. That would also explain why pressing the middle button of the mouse triggers this error, since linux uses mouse3 for copy/paste.
So my assumption is the Steam client has problems if you try to copy while there is nothing selected.
A few things to note:
I have Debian 8 "Jessie" use GNOME gdm3.
Nothing extracted yet.
Occasionally when navigating through pages in the browser frame (in both Community and Store), the mouse focus seems to get trapped within the browser frame.
When this happens, I can no longer click on any of the steam menu interface elements (such as the Steam-View-Friends bar or Store-Library-Community sections), nor any other windows, including those not managed by steam(!!). Trying to click and drag something in another window (or on empty desktop space), for example, will select text within the browser frame.
The only thing I know to do in this situation is switch to a tty and kill steam.
I'm on Linux Mint 17.1, using Xfce4.
It may be relevant that I have three monitors arranged horizontally. The primary monitor, which is usually where the steam window is, is in the middle (meaning that the left monitor is in the negative x-coordinate space).
I'm using Nvidia's proprietary driver.
This issue is intermittent, but occurs frequently enough that it happens to me at least once a day.