Expected, if you're inputting characters in a character set different from the one your database is set up to use. Unfortunately Mantis is not very good with character sets right now. See 0004084. Your best bet for now is to convert your database and your language files to UTF-8. Then it should work.

Thank you for taking the time to report a problem with mantis.

Since this problem report was originally made, a number of releases have occured. Additionally no recent feedback has been received on this issue.
It appears that this issue has either been fixed, or may not be a relevant report for the current release.

Unfortunately you are not using the latest version and the problem might already be fixed. Please download the latest release from http://www.mantisbt.org/download.php [^] [^]

If you are able to reproduce this bug in the current release, or have some more information on how this feature could be improved in the current release. Please either change the mantis version on this bug report
to the version you tested and change the status back to "Open", or open a new issue report with more information.

Again, thank you for your continued support and report.