redirect to empty page on preview button for new thread

I've been on LQ for a pretty long time and never had this happen before. I constructed about half of a new thread post for the slackware forum and wanted to see how it is shaping up, since the textarea input window is too small to see much of anything in. Instead of getting a preview, I get a page announcing some sort of browser check, and a captcha, which shortly redirects to a blank page. Nothing on the check page looks anything like any captcha I've ever seen. There's no way I can see to proceed with my post. Is this a known issue that will shortly be resolved? Is there some special requirement to be able to post in the slackware forum?