The rich text editor strips characters from the code block of a document in edit mode. To illustrate the issue, perform the following:

1. Open a new blank document for editing.
2. Click on the Wiki Markup tab in the editor (if it's not the default).
3. Enter the following in the content window of the editor:
This is: {code} a problem {+}, this is not

{code}
4. Click on the preview tab, you should see the the + symbol and 1 wrapped in braces within a code block, as intended.
5. Click on the Rich Text tab (no need to make any edits).
6. Click on the Preview tab again (the braces will now be removed from around the + symbol).

From what we can determine, the issue is associated with the functionality involving the Rich Text editor tab. As long as you avoid the Rich Text tab, you can bounce back a forth between the Wiki Markup and preview without this issue occurring.

The workaround is to set the Wiki Markup tab as the default and avoid the Rich Text tab altogether. If this cannot be fixed, then there should be a per user configurable option to remove the Rich Text tab from appearing in the editor so that one doesn't accidentally wipe out their edits as described. The Rich Text editor functionality essentially appears to be useless for all but the most basic text editing anyway.