Checklist

• I have searched the existing issues for similar issues.
• I added a very descriptive title to this issue.
• I have provided sufficient information below to help reproduce this issue.

Summary

With the introduction of accept_new_options, Streamlit uses the string value instead of the index internally to track selections. This means repeated labels aren't supported anymore

Reproducible Code Example

import streamlit as st

class foo():
    def __init__(self, a):
        self.a = a
    def __repr__(self):
        return "foo " + self.a
    def __str__(self):
        return self.a

options = [foo("a"),"a"]

c = st.multiselect("C", options=options)
c

b = st.multiselect("D", options=["A", "B", "B", "C", "C", "C"])
b

Steps To Reproduce

1. Run the app.
2. Select either of the two items in the first multiselect. In both cases, the first instance is selected and no further selection can be made.
3. Select "B" from the second multiselect and see that the second "B" can't be selected.
4. Select "C" from the second multiselect and see that the other "C" items can't be selected.

Expected Behavior

Before the introduction of accept_new_options these multiple items could be selected.

Current Behavior

No response

Is this a regression?

• Yes, this used to work in a previous version.

Debug info

• Streamlit version: 1.44.2.dev20250424
• Python version: 3.13
• Operating System: Mac
• Browser: Prisma

Additional Information

No response