Nastaleeq (ttf) subsetting missing ligature

Hi All,

My first post, so abt me:
I'm a programmer (c/c++/python/perl), but fonts are my hobby. So, please forgive me for any gaps in my knowledge on fonts.
I've successfully converted a free nastaleeq font to woff and am able to use it on my server and results are great.
Now, I'm trying to optimize the load time of the page, which is obnoxious given the fine nastaleeq font.
So, I got into subsetting. I'm using a script to subset based on text I'm going to send out, and the resulting font looks fine to me.
I checked it in FontForge and compared with the original to the best of my (sparse) knowledge. Things look OK to me.
However, the text that looks correct (using ligatures) with the original ttf or woff, renders with isolated forms with the subset font.