hinfsyn gamma<1 but sys is instable

Hi dear. I've encountered a weird problem. I setup a system G (uss format), then connected with the weighting functions and I got SYS (uss format). I used "hinfsyn" to calculate a controller K. The resultant gamma was less than 1(around 0.3). Then I used "robuststab" to analyse the stability and it was amazing that the system is instable.

clp_ic = lft(SYS,K_hinfsyn); omega = logspace(-2,2,300); clp_g = ufrd(clp_ic,omega); [stabmarg,destabu,report,info] = robuststab(clp_g,opt);

Normally, "gamma<1" means the close-loop system should be robust stable. But what I got was different.

Is there anyone who can help me out? Thanks a lot.