[syslinux] Isolinux command line text affected

[Михаил]

Hi!
This is my config file for isolinux
isolinux.cfg (
FONT /isolinux/font16.psf
NOCOMPLETE 0
default linux
prompt 1
timeout 600
display boot.msg
F1 boot.msg
F2 options.msg
label linux
  kernel linux
  append initrd=initram.gz vga=788 quiet
)
File boot.msg consist of some splash graphics and welcome message, and
option.msg is text only file.
After boot I types "linux" and press F2 to know more about useful
options (not press Enter key). But if I press F1 after it to back to
main screen, text line became affected (symbols changed). I press
Enter key and it says that kernel image not found.
This applies to isolinux version 3.70 - 3.80. Version 3.52 is fine.

Best regards, Mike.