Just a followup to confirm this appears to be due to a general bug with in-page vertical scrollbars in Chrome v.32:
http://code.google.com/p/chromium/issues/detail?id=335839
We've been able to reproduce that bug in various pages (not just ours) under Windows 7 only, and inconsistently at that, so there may be other contributing factors in play. I notice Google has already released a minor update to v.32.0.1700.102 -- to get that update, open Chrome, go to its main menu > About Google Chrome, which should start an auto-update if your Chrome isn't already current. Close and relaunch Chrome once it's done updating, then see if you can reproduce the bug; we're hoping Google issued a bugfix already.