bug(aria/listbox): selection state breaks when used with ngCombobox autocomplete (readonly=false)

[AdrianRomanski]

Is this a regression?

• Yes, this behavior used to work in the previous version

The previous version in which this bug was not present was

No response

Description

Selection state breaks with autocomplete and readonly set to false

When using ngListbox in multi mode inside an ngCombobox with autocomplete enabled (filterMode="manual" and readonly=false), the listbox selection state becomes inconsistent.

Important:

This issue does not occur when the combobox is set to readonly=true.

Video

Screen.Recording.2026-01-27.at.10.12.01.mov

Reproduction

StackBlitz link: https://stackblitz.com/edit/stackblitz-starters-tzi9ff2a?file=src%2Fcombobox%2Fcombobox.html

Steps to reproduce:

1. Create an ngCombobox with:
   a) filterMode="manual"
   b) default editable input (readonly=false)
2. Render an ngListbox with multi enabled inside the combobox popup
3. Select options sequentially from the list
4. Observe listbox()?.values() after each selection listbox = viewChild<Listbox<string>>(Listbox);

Expected Behavior

ngListbox in multi mode should

• preserve all selected values
• never reset selection unless explicitly cleared
• Combobox autocomplete input updates should not override or reset
• listbox multi-selection

Actual Behavior

Selection behavior is deterministic but incorrect

Every second selection

• listbox()?.values() resets to an empty array
• The combobox input value remains unchanged

Every third selection

The selected option becomes:

• the combobox input value
• the only value in listbox()?.values()
• This cycle repeats and makes listbox()?.values() unreliable for multi-selection state.

Environment

• Angular:
• CDK/Material:
• Browser(s):
• Operating System (e.g. Windows, macOS, Ubuntu):

[AdrianRomanski]

If there is a green light i would like to fix that :)