I was dinking around in the MATE Control Center and looking at the different options, and noticed that, under the "account type" item in the User Settings menu, my account type was marked as "Custom." Just to see what would happen, I changed it to "Administrator" - this led to me being unable to put my password in to any of the dialog boxes confirming administrator access. It turns out that, somehow, my password was reset to an empty string, such that I only had to press enter to authenticate myself.

I reset my password in the terminal (because of this issue) and tried swapping to a
"normal" user and back to admin as a test, and the password got set back to an empty string again.