Voice mode loses accurate PDF page context after switching from web chat

What issue are you seeing?

When I provide a PDF URL in the normal ChatGPT web interface, the model can correctly locate and discuss specific pages in the PDF. However, if I then switch to Voice Mode in the same conversation and ask it to continue teaching/explaining the PDF, it can no longer reliably locate the correct page and starts referring to the wrong slide/page content.

Example PDF:
https://cs231n.stanford.edu/slides/2025/lecture_5.pdf

In normal text/web chat, I can ask it to start from a specific page (for example, page 80) and it can identify the corresponding slide content accurately. After switching to Voice Mode, asking it to continue from a specific page often results in it describing content from a different page or otherwise losing the document position/context.

This makes Voice Mode difficult to use for interactive teaching over PDFs, because the conversation context appears to carry over but the document/page grounding does not remain accurate.

Steps to reproduce

1. Open ChatGPT on the web.
2. Send this PDF URL: https://cs231n.stanford.edu/slides/2025/lecture_5.pdf
3. In normal text mode, ask the model to locate and explain a specific page, e.g. page 80.
4. Confirm that it is discussing the correct slide/page.
5. Switch to Voice Mode in the same conversation.
6. Ask it to continue teaching from that page or move to a nearby specific page (e.g. page 81, 101, 104).
7. Observe that Voice Mode may identify the wrong slide/page or describe content that does not correspond to the requested page.

Expected behavior

Voice Mode should preserve the same PDF/document grounding available in the normal web conversation. If the text-mode model can locate page N accurately, switching to Voice Mode in the same conversation should allow it to continue referring to page N and subsequent pages accurately.

Actual behavior

After switching to Voice Mode, the model appears to lose or degrade its ability to resolve the PDF's page-level context, even though the conversation itself is preserved.

Why this matters

A major use case for Voice Mode is tutoring over lecture slides, papers, and textbooks. Accurate page-level continuity is essential: users should be able to say things like “continue with page 101” or “go back to page 80” without the model silently teaching from a different slide.

Environment

• ChatGPT web interface
• Voice Mode entered from an existing text conversation
• PDF supplied via public URL rather than uploaded directly
• Reproducible with Stanford CS231n Lecture 5 (2025) PDF above

I realize this repository is primarily for Codex, but I'm reporting it here because this appears related to context/tool parity across ChatGPT interaction modes and there may not be a more appropriate public issue tracker.