Consider that "admin" has "create issues, modify reporter" permissions; "johny" has "create issues" permissions;
I am logged in as "admin".

1) Following script runs successfuly but has no effect (issue is not created)

<JiraJelly xmlns:jira="jelly:com.atlassian.jira.jelly.enterprise.JiraTagLib">
<jira:Login username="admin" password="admin">
<jira:CreateIssue project-key="SS" summary="Some desc" issueType="Bug" fixVersions="1.0" reporter="johny" />
</jira:Login>
</JiraJelly>

2) Trying this one I get (localized) message "you have no modify reporter permission"...

<JiraJelly xmlns:jira="jelly:com.atlassian.jira.jelly.enterprise.JiraTagLib">
<jira:CreateIssue project-key="SS" summary="Some desc" issueType="Bug" fixVersions="1.0" reporter="johny" />
</JiraJelly>

result:

<JiraJelly xmlns:jira='jelly:com.atlassian.jira.jelly.enterprise.JiraTagLib'>
<Error action='CreateIssueDetails'>
<TagContents>((summary=Some desc)(issuetype=1)(fixVersions=10050)(issueType=Bug)(reporter=johny)(project-key=SS)(priority=3)(pid=10050))</TagContents>
<ExecutedAs>user=johny</ExecutedAs>
<ErrorMessage>
Result=input
Nie masz uprawnień do zmiany zgłaszającego sprawę.
</ErrorMessage>
</Error>
</JiraJelly>

Who has to have this permission?
a) "johny"? he creates issue, he does not "modify reporter"... he is reporter. Documentation says that "reporter" attribute is "The username of who is reporting this issue, the user is logged in and then the issue created".
b) "admin"? he has that permission (he is in "global-admins" group which is attached in "SS-ps" permission scheme as "modify reporter"; that scheme is used in "SS" project").

So... what is wrong?

BTW. Following script works because I need to create issues for testing purposes and I know johny's credentials:

<JiraJelly xmlns:jira="jelly:com.atlassian.jira.jelly.enterprise.JiraTagLib">
<jira:Login username="johny" password="johnypass">
<jira:CreateIssue project-key="SS" summary="Some desc" issueType="Bug" fixVersions="1.0" />
</jira:Login>
</JiraJelly>