Visual View doesn't reflect the changed Source View

### Apache NetBeans version

Apache NetBeans 19

### What happened

When running a project created in accordance with the "File Type Integration Tutorial" and changing the Source code and saving on the Visual tab, no changes occur and an unexpected interruption is shown "A org.openide.util.RequestProcessor$SlowItem has occurred"

### How to reproduce

1. Create a project according to the "File Type Integration Tutorial" (https://netbeans.apache.org/tutorials/nbm-filetype.html)
2. Launch the project.
3. Create a Java application and create a file of a given type (all in accordance with the "File Type Integration Tutorial")
4. Change the file in the "Source" tab and save the project

### Did this work correctly in an earlier version?

No / Don't know

### Operating System

Windows 11

### JDK

1.8

### Apache NetBeans packaging

Apache NetBeans provided installer, Apache NetBeans platform

### Anything else

_No response_

### Are you willing to submit a pull request?

No

Start by reproducing the project from the File Type Integration Tutorial, then trace the Source and Visual tab interaction that produces the RequestProcessor$SlowItem interruption after saving. Done means changes saved in Source View are reflected in Visual View without the interruption.

Written by the indexing model from the issue text.