The SPOJ MST problem is in the partial section, not in the classical section.
(see topmost left " Problems /partial/ Minimum Spanning Tree" )
As you might have known, partial problems in SPOJ do not show whether you are AC or WA or such, yet it shows how many percentage of the test cases you are correct. If it showed 100 then congrats you passed 100% of the test cases. Hope this helps