I'm cannot be certain if this script did work previously and this is just a incompatibility with the newer version of NSIS or if it always behaved in this manner.
Vytautas!macro InstallFont FontNAME Index
SetOutPath $FONT_DIR
IfFileExists "$FONT_DIR\${FontName}" ${Index}
File '${FontName}'
System::Call "GDI32::AddFontResourceA(t) i ('${FontName}') .s"
${Index}:
!macroend