Ran into the same thing. Simple workaround is to stop the inline, add the </>, and continue the inline (ending it at the next </> and resuming it afterward).

(ampersand)abc <123> xyz(ampersand) results in @abc <123> xyz@

(ampersand)abc(ampersand) <(ampersand)123(ampersand)> (ampersand) xyz(ampersand) gives you @abc@ <@123@> @xyz@, which is what you want.
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Sorry -- "@" is not an (ampersand). Also, "add the ," should be "add the < or > characters," (if you follow a less than immediately by a greater than, redmine appears to not show it).
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The problem is redcloth parses twice these characters ; the first time it escapes all "<" and ">", no problem about that, but the second it traduces resulting "&amp;lt;" to "&amp;amp;lt;" (and so on), which is incorrect. It seems to me it's a redcloth problem, so I patched recloth lib to avoid second parsing. See attachment and let me know your opinion about that.
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This works fine for inline code with @ separators. For <pre> </pre> separators, this does not work.
Why not considering moving to RedCloth 4 that apparently fixes these 2 issues ?

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This works fine for inline code with @ separators. For @<@pre@> separators, this does not work.
Why not considering moving to RedCloth 4 that apparently fixes these 2 issues ?

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In fact, the bug I described (with pre separators) appears when I use coderay-0.9.1 (for java syntax coloration) that I have copied manually in redmine/vendor/plugins.
I attached a patch of redcloth3.rb that seems to work.

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Anthony Groyer wrote:
> In fact, the bug I described (with pre separators) appears when I use coderay-0.9.1 (for java syntax coloration) that I have copied manually in redmine/vendor/plugins.
> I attached a patch of redcloth3.rb that seems to work.

This patch solves the issue when the < and > are between a <pre><pre><code class="..."> </code></pre></pre> tags but create a bug when they are used in <pre><pre> </pre></pre> tags.
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The initial defect (< > inside inline code) is fixed by applying Jean-Baptiste's patch in r3567.
Anthony, your problem seems different and your patch breaks a few tests.
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I do have about the same problem with lines starting with a space
like this

<VLAN>
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duplicates,Closed,2280,lesser symbol is printed as HTMLcode
duplicates,Closed,3020,Problem with wiki formatting for inline code with "@" characters
duplicates,Closed,2922,bad escaping of < and > in code exemple in redmine Wiki
duplicates,Closed,4794,wiki rendering bug