Is it starting/ending game downloads when this happens?
Nope.
I can reproduce this on KDE 5.8.5 and 5.9 on Xorg. I have not tried earlier versions of KDE, and I have not tried KDE on Wayland.
Seems to be sometimes reproducable with other circumstances too, such as opening and closing the friends list making the main window demand attention, but the listed steps seems to be the most reliable.
Edit: Temporarily switching KDE's window manager to xfwm4 (XFCE's window manager) with the command xfwm4 --replace seems to have stopped this issue from happening. It is most likely a problem between Steam and kwin.
Edit 2: I think this is the relevant message from kwin's terminal output when following the above steps.
QXcbConnection: XCB error: 8 (BadMatch), sequence: 15299, resource id: 71303454, major code: 42 (SetInputFocus), minor code: 0
Today's steam beta client has "Fixed Windows taskbar showing pending progress even if there are no more needed updates" which has a small chance of being related to this issue. Can someone test for the quirk behavior with the steam beta client.
It might have fixed one of multiple causes but definitely not all. So far I haven't had it randomly turn orange while I'm doing other stuff, but when I accidentally closed the Steam client main window, the Friends tab turned orange.
This issue have been pestering me for quite a time (year or so I think). My workaround it to use KWin's shortcut "Switch to window demanding attention" to switch to steam and "dismiss" the orange highlight.
Just popping in to let you know this is still happening in 17.04 with the new Plasma.
I'm starting to wonder if this is related to Steam's habit of focusing other client windows when one is closed. For example, (in Windows) when I get an event notification and then close it, the main client window pops into the foreground even if it was behind something else like Firefox. It's possible that Linux window managers are (understandably) blocking this behavior and using the orange taskbar behavior as a way of saying "Hey, this program wants your attention, but you're going to have to click it yourself."
Yes, one option is that window simply "asks attention" - _NET_WM_STATE_DEMANDS_ATTENTION which makes orange taskbar entry. Another one is sending _NET_ACTIVE_WINDOW - ask to activate some window, but window manager might deny it and just set _NET_WM_STATE_DEMANDS_ATTENTION instead.
Yeah, I think this is now only happening when I close one window and another tries to take focus. Arguably that's a different issue than what I was describing, which is that it was happening completely at random. But it's also a cross-platform issue, which means it's not appropriate for this place. Should I close this, or what?
Plasma 5.18.5, and the issue persists.
Oddly enough, it often happens to an already-focused window, and clicking on it again does nothing; to remove the orange highlight, you need to switch focus to another window, then select the "orange" one again. In case of the main client window, hovering the cursor over one of the drop-down menus (Store, Library, Community, etc.) works as well.
P.S.: Here's an easy way to reproduce the rogue highlight: focus the Steam client window, open the settings (Steam -> Settings), focus some other non-Steam window, minimize it (the focus will return to the settings window), close the settings window. This should left the client window stuck in the pseudo-focused "highlighted" state.
Apparently, something has been fixed at some point, as I haven't seen this issue manifesting in a while. (Plasma 5.24.5 here.)
Closing per the last comment.
Nothing extracted yet.
I recently got back onto my Linux build, updated Steam (big ups to whoever took over the Linux client, by the way; I saw all the fixes in the latest patch notes!), and ran a full system upgrade from 16.04 to 16.10. And I'm noticing some behavior I wasn't seeing before, although maybe I just didn't notice it: The taskbar button for Steam sometimes turns orange for no apparent reason. I thought maybe it was accidentally doing this whenever it generated a toast saying a friend had launched a game, but no. It might be doing it in response to friends quitting games or going offline, which don't generate toasts; I'm having a hard time constantly monitoring the Friends pane without falling asleep.