So, I finally figured out the real problem causing all of that stuff I experienced in this thread: the HDD on this machine was failing (according to the drive's SMART info, it had 7.6 years of spin time, and was failing about 50% of all operations on the first try, though it was not obvious there was an issue because it was almost always succeeding in the first few retries so did not return a fail state to the OS), and as it's got kinda minimal RAM (256mb), the swap space on the HDD was seeing heavy use. Heavy use of the failing HDD as virtual memory is, of course, likely to generate all sorts of funny problems as occasionally something in memory gets corrupted. Since replacing the HDD about a month ago, all such symptoms disappeared.
Anyway, sorry for resurrecting this zombie thread, but I wanted to post what the actual issue was and the solution.
Tom