Display mode 0x6 doubles lines

Host environment

• Operating system: manjaro
• OS/kernel version: 5.15.32-1-MANJARO
• Architecture: x86-64
• QEMU flavor: qemu-system-i386
• QEMU version: 6.2.0
• QEMU command line:

  qemu-system-i386 -option-rom optionrom.bin -netdev tap,id=ne,ifname=tap0,script=no,downscript=no -device ne2k_isa,iobase=0x300,irq=5,netdev=ne   

Emulated/Virtualized environment

• Operating system: NO_OS
• OS/kernel version:
• Architecture: i386

Description of problem

When developing https://github.com/korneliuszo/ne2000xt I've occured problem with double lines in mode 0x06 of VGA display, problem doesn't exist in mode 0x05

Steps to reproduce

1. Call int 0x10, to setup video mode
2. put data into video ram (./cga.py -i 192.168.1.102 -I ~/a.png)
3. bad display

Additional information

Bad display:

Same data, but in mode 0x05

Same script as in bad display but run under 86Box