Equation Editor unexpectedly appears to merge separate inline equations and any content between them when editing

## Description

When editing a sentence containing multiple equations, the Equation Editor exhibits unexpected behavior that appears to merge separate equations.

A video demonstrating the issue is available: [Video: Equation Editor unexpectedly merges separate inline equations and any content between them when editing (2 minutes)](https://iu.mediaspace.kaltura.com/media/t/1_0ux0ciar)

### Steps to Reproduce

1. Type the following sentence in Word, using the Equation Editor for the mathematical expressions:
"The expressions $`4+5`$ and $`6+4`$ are equivalent."

2. Place the cursor at the end of the first expression (after "5")

3. Press the backspace key

### Expected Behavior

- When backspacing in the first expression, the Equation Editor should remain confined to just that expression
- The second expression should remain separate and independent
- Moving through the text should treat each expression as distinct

### Actual Behavior

- Pressing backspace causes the Equation Editor to unexpectedly expand and merge both expressions
- The Equation Editor grows to encompass everything from the first expression through the second expression, including the text between them
- When navigating:
- With cursor in either expression: Both expressions and intervening text are shown as merged in the editor
- With cursor between expressions (e.g., in the word "and"): Equation Editor disappears entirely

### Impact

This behavior:
- Makes it difficult to edit individual expressions
- Creates confusion about which parts of the text are part of the equation
- Disrupts the normal flow of document editing
- Could lead to unintended changes when trying to make simple corrections

# Tested Version Information
## Windows OS
OS Version:
-- OS Name: Microsoft Windows 11 Enterprise
-- Version: 10.0.22621 Build 22621
-- Locale: United States
Microsoft Word Version:
-- Microsoft 365 Apps for enterprise
-- Version 2410 (Build 18129.20158 Click-to-Run) Current Channel