removing spell syntax highlighting in vim

removing spell syntax highlighting in vim

This question is a sequel question of this one. I have the following
script that removes capitalized words from vim spell check.
syn match myExCapitalWords +\<\w*[A-Z]\K*\>+ contains=@NoSpell
But it works only if I do syn clear first. But then all other highlighting
(e.g. markdown) gets lost. I went through syn list to see what might be
causing the conflict, but now I am out of clue.