Valve note: works correctly for me.
I had something similar a couple of months back and it was because of a corrupted user profile in Ubuntu, I logged out, found my user profile, renamed it and logged back in with all my details, (all my settings were reset) and it worked.
That seems likely, @Sarkie. @DynamicBits does steam output anything like my line below on launch when its run from the terminal? If so, deleting the file ClientRegistry.blob in your Steam dir would fix it.
KeyValues Error: RecursiveLoadFromBuffer: got EOF instead of keyname in file UserLocalConfigStore [offset: 49152]
UserLocalConfigStore, apptickets, 206690, (41800), (CDDialog), (NameHistory),
The terminal output does have many lines like that. Deleting ClientRegistry.blob didn't seem to have any effect on those messages or my original problem.
However, your suggestion prompted me to look into that specific message about UserLocalConfigStore, which led me to issue #2281, where you recommended backing up and deleting steam/userdata/*/config/localconfig.vdf. I did that and everything works now. The original file was truncated to 4,096 bytes. While my problem is solved, I feel that something more could be done to either automatically fix the issue, or at least notify the user of the problem (without requiring launching from a terminal).
On a side note, there were 51 different directories in userdata. I am the only Steam user on this computer, so that seemed a little odd to me.
Nothing extracted yet.
I previously had "+connect 127.0.0.1" in the launch options for most of my HL1 mods. At some point (at least a month ago) the launch options seem to have been cleared. I am currently unable to add anything back to the launch options for any game.
Steps to reproduce: