The "Trusted file locations" one can enter in
  Tools|Options|OpenOffice.org|Security|Macro security|Trusted sources
seem to be case-sensitive.

That is, if you enter "C:\trusted" as trusted source, and open a document
containing macros from "c:\trusted", the document is recognized as being
insecure, though it should be secure.

Especially with drive letters, this is annoying, since OOo seems to have a
non-deterministic way to use upper or lower case drive letters (for instance, I
often have two entries in the "recent file" list for the same file, one with
upper case, one with lower case driver letter).