I don't understand what you mean.
Please add screen shots of what you entered and what you get after it's rendered via Markdown.

Check also, if there is any other open issue in category markdown which might be a duplicate of your issue.

BTW, quellcode is very German ;-)

I hoped to reproduce the markdown bug here in the description.
Now i have postet the screenshot. The text of the description is System.out.println("Hello World"); It should show the " and not the html tag (")

Maybe i can reproduce it here in the comment:
System.out.println("Hello World");

2017-08-11-Markdown.png (1,929 bytes)   

2017-08-11-Markdown.png (1,929 bytes)   

Did you change any source of MabtisBT or did you install any 3rd party plugin?

Do you see any errors or warnings when running admin/check/index.php?

We are using the following pugins:
Email Reporting 0.10.0-DEV
Jquery Chosen 0.3
Source Control Integration 2.0.3
Source Subversion Integration 2.0.0

With admin/check/index.php we got no errors and some warnings.
Many of them from obsolete config or and wrong Paths.
This is the only warning i cant interpret something in:
Browser Search engine names must be 16 chars or less
Either shorten the "search_title" configuration option to a maximum of 11 characters, or alter the "opensearch_XXX_short" language strings as appropriate to meet the OpenSearch 1.1 specification for the ShortName element.

Are you able to reproduce the issue with a fresh install of MantisBT 2.5.1 without any installed 3rd party plugins?

I installed a fresh mantisBT 2.5.1 without any 3rd party plugins and didnt get the error.
Then i installed alle the plugins and didnt get the error.
So Mantis is working fine with Markdown and the error has something do to with the Pluings or our installation.

Thanks for the help.

Thanks for the feedback.

The error happens again. I have a fresh installed Mantisbt 2.19.0 with markdown activated ( Manage Plugins -> MantisBT Formatting 2.19.0 -> Markdown Processing -> ON).
Now i want some source code thats starts with and ends with. In this Block i want to add " or <. These 2 symbols aren't converted.

Information to the System (Manage -> Site Information )
MantisBT Version 2.19.0
Schema Version 209
PHP Version 7.1.24-1+0~20181112093455.10+stretch~1.gbp09a4fd
Database Driver mysqli
Database Version, Description 5.7.22, 5.7.22-1

In these 2 Screenshots you can see where the problem is.

EditNote.png (7,859 bytes)   

EditNote.png (7,859 bytes)   

Activities.png (8,940 bytes)   

Activities.png (8,940 bytes)   

@neumann I assume you are now encountering 0024628
Right?

Yes thats the same Problem. The only thing i have to add is that < in nowhere mentioned .