I was right! Over in
http://www.gnutellaforums.com/showth...&threadid=9371, Christopher Rohrs says:
<blockquote>We just discovered a bug where LimeWire can delete incomplete files immediately, making resumes impossible. The problem happens if you set the "keep incomplete files" option to anywhere between 24 and 49 days. Values between 75 and 99 days will also have the same effect, as will some other values. The problem is caused an overflow error.</blockquote>
He thinks a fix will be in 2.4. Meanwhile, he suggests the default of 7 days should eliminate the problem. My 999 seems to as well, if you need something longer!