Why doesn't install-strip strip shared libraries sometimes

[Yuri]

I came across one project in which install-strip doesn't strip the 
shared library: liblink-grammar.so in 
https://github.com/opencog/link-grammar

As an opposite example, showing the normal behavior, install-strip 
strips libexpat.so in 
https://github.com/libexpat/libexpat/tree/master/expat.


What might prevent install-strip from stripping liblink-grammar.so?


Thanks,

Yuri