Input in template substitution window requires template names to be escaped (ie. those with parenthesis), otherwise the substitution doesn't work.
If I want to have template "Infobox Hokejista (nehrající)" subst'd, my input needs to be "Infobox Hokejista \(nehrající\)". However, the result is not {{subst:Infobox Hokejista (nehrající) but {{subst:Infobox Hokejista \(nehrající\).