After the restart, windows and avast! loaded up normally and the avast! GUI listed my database (still 110801-1) as current. I clicked for a manual update and the GUI responded with the usual “your definitions are already up to date” message.
Since this happened, I’ve ran a couple scans that went normally and the definitions have updated automatically with no issue (I also ran a MBAM scan that came up clean). The installer I had used was for program version 6.0.1125, which I then updated to 1203 via the GUI. The MD5 of the installer matches the one listed on filehippo.
My concern is that it may be indicative of a problem with my installation. This was the only time I’ve ever had this happen, so I’m hoping its just a fluke.