How to get rid of oddly-highlighted keywords in Vim

For what it's worth, I am using Vim for a Grails project, written in Groovy, and I have the Groovy plugin[1] installed. There are certain keywords ("delete" is one) that for some reason are highlighted in red wherever they occur in my source files. What might be the reason for this? I don't think it's the Groovy plugin, because this was occurring back before I had it installed. Also: How might I get rid of this highlighting?

[1] http://www.vim.org/scripts/script.php?script_id=2217

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