The mantisbt ebuild removes the adodb that comes packaged along with the release tarball which breaks the SOAP API:
[Wed Apr 25 06:58:28 2012] [error] [client 192.168.21.204] PHP Fatal error: require_once() [<a href='function.require'>function.require</a>]: Failed opening required 'adodb/adodb.inc.php' (include_path='/var/www/localhost/htdocs/mantisbt/core/:/var/www/localhost/htdocs/mantisbt/library:../../library') in /var/www/localhost/htdocs/mantisbt/core/database_api.php on line 35
Adding a symlink to the system adodb in mantisbt/library seems to resolve the issue.
I don't know what the correct fix for this issue would be but as last resort it would be nice if the ebulid could put the synlink in place while installing, maybe?
I do not know if it is related to this bug, however i had a problem not being able to use mantisbt after upgrade to 1.2.8 due to wrong/bad adodb file placement.
basically it was looking for some files in /usr/share/php/adodb/drivers but the required files were in /usr/share/php/adodb so i added symlink and created a loop.
this is not in the tree anymore