For some time we've been getting reports of weird problems with Internet Explorer 8 (IE8). A few weeks ago we got around to fixing most of these problems, which were caused by IE8's buggy 'range' function (which is what Wikidot uses when you select text and then click the Bold icon or press Ctrl-B).
Today we finally found the other problem (skipping cursor on larger pages), which was - surprise - another IE8 bug. this thread on grantovich.net explains it.
Update: the IE8 editor is broken when it comes to textareas and our fix did not work on all pages. This affects lots of websites, not just Wikidot. It specifically hits when you style the textarea to fit the page width, and use long lines of text that poor IE8 has to wrap. Microsoft have promised us personally that they will fix this in Windows 7, and are organizing parties to celebrate this fix.