My Solution

[mullr]

After much pain and strife, I solved the problem. As I suspected, it was not the part of any of my code. Rather, it was a configuration issue, my own fault, not the upgrade's.

First, there were some other symptoms that turned out to be related to the problem.

Qt applications would show up incredibly huge. This was not a big problem, nor did I notice it right away because I seldom use those programs.

Some Tcl/Tk programs exhibited the same behaviour as the Qt programs. The also showed the scrollbar wierdness that I originally saw.

After thinking about this for awhile, I realized that I had been mucking with my X configuration a little, but I had dropped it and never finished with it. Since my oft-used applications were not affected, I didn't link it to the problem. But, upon removing  Load  "xtt" from the "Module" section of my XF86Config, all of the problems vanished.

Ah, lessons learned.

See you, space cowboy