natural sign before g'' in combination gis' g''

[Albert Einstein]

Why lilypond don't put natral before g'' in combination gis' g'' ?

a'\mf gis' a' \< <a'  I want hier natural -> g'' >~ <a' g''>  <a' f''>8 
< a' c''>16  % bar
< g' e''> dis'' e''\! a''~ a'' c''' g'' e''  % bar
<fis' c''>8 <fis' c''> <hier lilypond puts natural-> f' b' e''>16\> <f' 
b' d''>8 < e' g' c''>16~\! }    %bar

see picture