Whatever I type to the search field, it seems its case does not matters, it is converted to lowercase and then matched against the desktop files in case sensitive mode. Hence it will never match an uppercase letter in the desktop files. For example, I have a quadra.desktop file containing Name=Quadra. If I search for "quadra", "Quadra", "QuAdRa" etc., there's no match. If I search for "uadra", "UaDrA" etc., it matches. If I change the desktop file to contain Name=quadra, then all the searches mentioned above match.
Created attachment 175 search patch 1 Proposed patch to fix the problem (against xfce4-appfinder-4.2.0.tar.gz)
Created attachment 176 search patch 2 This does NOT necessarily pertain to this bug, so I submit it separately. The problem is when the .desktop Name and Comment do not include the name of the actual program. For example, gaim is known as "IM" on Redhat systems, and has a comment of "Multi-protocol Messaging Client"; so when you search for 'gaim', you get no hits. This patch will search the exec path as well; so that you can find applications like this. (this patch also includes the changes in comment #2)
Patch applied, thank you!