I now believe that this is a bug in the fonts. It is still a mystery to me why this problem only occurs in the Debian build, though.
Please forward this bug to ttf-freefont, and upgrade severity to important. In the freetype fonts, the OpenType feature tag for the Alef-Lamed ligature (0xFB4F) is "liga", which means "Standard Ligature". That implies that the ligature is mandatory. But this ligature certainly should not be mandatory. The correct feature tag for this ligature should be "dlig", which means "Discretionary Ligature". See the OpenType specification document for Hebrew at: http://www.microsoft.com/typography/otfntdev/hebrewot/features.aspx When I make this change in the SFD source file and recompile using fontforge, the problem is fixed.
