(LINUX Vulkan) black vulkan app window switch back to vtx from vt7

i installed driver390.87 and nvidia-vulkan-icd vulakninfo etc on debian9 stable. dual video card intel+k1100m.

vt7 running defualt desktop using intel video card as primary cideo card. start another xserver on vt2 with configure k1100m as the priamy video card, running vulkan-smoketest and glxgears on the seconde xserver looks good.

the problem is running vulkan-smoketest, then switch to vt7 and switch back again, the vulkan-smoketest window totally black never restore, the glxgears window restore quickly.

so the driver’s vulkan part has bug? or make some config with the kernel module loading or nvidia xorg conf?