Markdown Table multicolumn header removed when switching to visual editor from source

Bug description

When switching between visual editor and source editor the formatting of markdown tables gets changed. Particularly when there is a multicolumn header it is removed and a | is placed in make the columns not multicolumn.

In source mode:

---
title: "Try turning on Visual"
format: html
---

+------------------------------------+--------------------------------------------+--------------+
|                                    | Decision (Conclusion from hypothesis test)                |
+====================================+============================================+==============+
| True Population                    | Reject $H_o$                               | Accept $H_o$ |
+------------------------------------+--------------------------------------------+--------------+
| Means are equal ($H_o$ is true)    | $\alpha$                                   | 1 - $\alpha$ |
+------------------------------------+--------------------------------------------+--------------+
| Means are unequal ($H_o$ is false) | 1 - $\beta$                                | $\beta$      |
+------------------------------------+--------------------------------------------+--------------+

After switching to visual mode and back

---
title: "Try turning on Visual"
format: html
---

|                                    | Decision (Conclusion from hypothesis test) |              |
|-------------------------|-------------------------------|----------------|
| True Population                    | Reject $H_o$                               | Accept $H_o$ |
| Means are equal ($H_o$ is true)    | $\alpha$                                   | 1 - $\alpha$ |
| Means are unequal ($H_o$ is false) | 1 - $\beta$                                | $\beta$      |

Rstudio version: "Spotted Wakerobin" Release (7872775e, 2022-07-22) for Windows

Checklist

• Please include a minimal, fully reproducible example in a single .qmd file? Please provide the whole file rather than the snippet you believe is causing the issue.
• Please format your issue so it is easier for us to read the bug report.
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