We are aware of this issue and we plan to fix it in a future RadEditor release. For now, the only workaround we can offer you is to change the editor type to "Enhanced Rich Text", which will allow Safari to use the formatting options. Open the Tasks list settings page and click on the Description column, which is of type "Multiple lines of text". On the "Change Column" page, click the "Enhanced Rich Text" radio button and finally click "Ok" (see attached screenshot).
Here is some additional information, if you want to learn about the specific issue: Online HTML editors like RadEditor rely on the browser's internal rich text engine in order to allow for editing content. Commands like Bold, Underline, Font-Color, etc. are passed directly to the browser engine, which renders the appropriate HTML. All browsers except Safari can be set to use HTML tags like <strong>, <em>, etc. to represent formatted text (bold, italics). Safari always uses CSS instead of HTML tags - e.g <span style="font-weight:bold"> for bold. Unfortunately, the basic MOSS text editor does not allow CSS formatting, which means that all Safari CSS content will be stripped when you save the page. Copied content from other browsers will not be changed because it does not contain the forbidden CSS styles. The MOSS content filters that do the stripping are called after the editor content is submitted, which means we cannot bypass them. Here is the relevant Safari Bug tracker issue - https://bugs.webkit.org/show_bug.cgi?id=13490
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