Your statement is too general as the problem seems to depend on the kernel. I will try to clarify based on my experience, which is not exhaustive by any measure:
Qemu is fixed in Cosmic (18.10) 64-bit running kernel 4.18.0-11-generic (but does NOT work in kernel 4.18.0-10-generic). I did not try it in Cosmic (18.10) 32-bit or any other 64-bit kernels.
Qemu works in Xenial (16.04) 32-bit running kernel 4.4.0-119-generic or 4.8.0-58-generic but does NOT work with any other kernel I tried. I did not try it in Xenial (16.04) 64-bit.
Qemu does NOT work in Bionic (18.04) 32-bit with any kernel I tried. I did not try it in Bionic (18.04) 64-bit.
Andreas,
Your statement is too general as the problem seems to depend on the kernel. I will try to clarify based on my experience, which is not exhaustive by any measure:
Qemu is fixed in Cosmic (18.10) 64-bit running kernel 4.18.0-11-generic (but does NOT work in kernel 4.18.0-10-generic). I did not try it in Cosmic (18.10) 32-bit or any other 64-bit kernels.
Qemu works in Xenial (16.04) 32-bit running kernel 4.4.0-119-generic or 4.8.0-58-generic but does NOT work with any other kernel I tried. I did not try it in Xenial (16.04) 64-bit.
Qemu does NOT work in Bionic (18.04) 32-bit with any kernel I tried. I did not try it in Bionic (18.04) 64-bit.