Cannot see plot with qt graphics_tool kit on octave-6.4.0

[Tatsuro MATSUOKA]

I cannot see a plot with qt graphics_toolkit.

>> graphics_tookit qt;
>> plot(1:10);

plot window is filed with black.

I met this on two different PCs.

On one PC,
>> plot(1:10);
Xlib: sequence lost (0x11a61 > 0x1a63) in reply type 0x0!
Xlib: sequence lost (0x11a76 > 0x1a78) in reply type 0x0!
Xlib: sequence lost (0x11ab4 > 0x1ab6) in reply type 0x0!
Xlib: sequence lost (0x11afc > 0x1afe) in reply type 0x0!
Xlib: sequence lost (0x11b12 > 0x1b14) in reply type 0x0!

But on the other PC, the above messages do not appear.

Tatsuro