Launcher downloads update every time it's invoked.

Lately, every time I start up the launcher, it goes through the update downloading process, even if I immediately close and reopen the launcher (thus eliminating the possibility that there's just been a lot of updates lately). It feels to me like the launcher doesn't correctly note that it's been updated, so every time it starts it feels the need to download a bunch of things.

I should note that the launcher itself works just fine, allowing me to start up Minecraft like it should. It just insists on spending a lot of time downloading stuff it should already have.

I've attached the launcher log (launcher_log.txt), as well as the terminal output (launcher_termout.txt) from my still-running launcher instance (since it seems a lot of information is missing from the log file itself). The C++ error at the end of the terminal output is just included for completeness, but it came long after the launcher finished its update routine.