Quickly inserting css and js often fails to work

Source zip for testing.
[reproduce.zip](https://github.com/apache/netbeans/files/12034163/reproduce.zip)

### Apache NetBeans version

Apache NetBeans 18

### What happened

work fine

https://github.com/apache/netbeans/assets/137764/a0ba3e88-f462-430a-8ebc-ebbd815a4a5e

it doesn't work

https://github.com/apache/netbeans/assets/137764/03143bd8-1025-41a3-92eb-43dbdd0c7914

### How to reproduce

I don't know how to reproduce,maybe its own fault.

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

No / Don't know

### Operating System

wondows 10 and windows 7

### JDK

19.0.2

### Apache NetBeans packaging

Apache NetBeans binary zip

### Anything else

_No response_

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

No

Start with the attached reproduce.zip and the two reported behaviors in Apache NetBeans 18 on Windows with JDK 19.0.2, comparing the working and failing insertion shown in the linked recordings. Because the report provides no reliable reproduction steps, first identify a repeatable sequence; done means quickly inserting CSS and JavaScript works consistently.

Written by the indexing model from the issue text.