Alt+Up in TextBox adds an X character

[Leopard20]

Describe the bug

Pressing Alt, then Up, then releasing Alt prints an "X" character in TextBox.

To Reproduce

1. Create an Avalonia UI project.
2. Create a Window. The contents can simply be:

<Grid>
	<TextBox Text="Hello"></TextBox>
</Grid>

3. Run the project and focus (click on) the textbox.
4. Press and hold Alt
5. Press Up
6. Release Alt
7. An "X" appears in the textbox

Expected behavior

No character should appear.

Avalonia version

11.2.3

OS

Windows

Additional context

No response

[timunie]

Additional notice: It only reproduces when there is some text before. An empty TextBox doesn't reproduce. However the numerical [ALT] + [0 ... 9] also don't work in that case.

[Leopard20]

Actually I managed to reproduce it with empty TextBoxes too. I don't remember how but I'll try again and if I find it I'll post it here.

[samtun]

Alt + Left/Right/Down also produce symbols for me:
(Left, Down, Right, Up)
,▬BX

ALT + Numpad shows similar behavior. Maybe this is somehow interpreted as ASCII symbols which can be input via ALT + Number (e.g. ALT + 0088 for X)?

[Gillibald]

Yes pressing alt and typing a valid ascii code is a Windows feature. Not sure if other platforms do the same.

[mgarstenauer]

As mentioned in #18326: This bug also breaks the rectangular text selections in AvaloniaEdit. AvaloniaEdit uses Shift+Alt+Arrow keys for rectangular selections. The user tries to make a rectangular selection, suddenly the selection is replaced with unexpected characters.

This bug doesn't always trigger – the order in which keys are released matters.