Wrong key events when Num Lock is active

[klpn]

If Num Lock is active, key events like Num Lock+<key> are generated when e.g. arrow keys are pressed.

To Reproduce
Steps to reproduce the behavior:

1. Run kitty +kitten key_demo with Num Lock activated.
2. Press and release left key (not on the numeric keypad). This gives the output.

NumLock+LEFT PRESS 
CSI 1 ; 129 D
NumLock+LEFT RELEASE 
CSI 1 ; 129 : 3 D

Expected behavior
Should generate an event pair like

LEFT PRESS 
CSI  D
LEFT RELEASE 
CSI  ; 1 : 3 D

The significance of the problem is that I cannot use the arrow keys to navigate in the Unicode Input kitten's name mode when Num Lock is active. They work fine when Num Lock is not active.

Environment details
OS: Arch Linux

$ kitty --debug-config
kitty 0.20.2 created by Kovid Goyal
Linux karl-ThinkPad-T580 5.11.16-arch1-1 #1 SMP PREEMPT Wed, 21 Apr 2021 17:22:13 +0000 x86_64
Arch Linux \r (\l)
LSB_VERSION=1.4
DISTRIB_ID=Arch
DISTRIB_RELEASE=rolling
DISTRIB_DESCRIPTION="Arch Linux"
Loaded config files: /home/karl/.config/kitty/kitty.conf
Running under: X11

Config options different from defaults:
background            Color(red=255, green=255, blue=234)
font_size             12.0
foreground            Color(red=0, green=0, blue=0)
update_check_interval 24.0
url_prefixes          ('http', 'https', 'file', 'ftp')

Additional context
The problem can be reproduced with kitty --config NONE