If a project has issue-level security scheme assigned, and a user has set-security-level permission, security level is required to create an issue. This makes it impossible to create an issue through SOAP, because RemoteIssue doesn't provide such field.

More specifically:
a) if I try to create an issue as usual, I get an error saying "security level is required".
b) any ways to pass security level to the server fail, including specifying custom field of name "security" or specifying <security> tag in the SOAP request.

Interestingly, I can change security level through SOAP's updateIssue request because it doesn't use RemoteIssue.