The first issue you identified is just that your Intel GPU is too new for Linux kernel 4.13 so you need to set alpha_support=1. This will be fixed in Linux kernel 4.15 (coming in Ubuntu 18.04).
The second issue you describe is bug 1724732. So let's keep this bug just about the first issue.
Thanks, that's a nicely detailed bug report.
The first issue you identified is just that your Intel GPU is too new for Linux kernel 4.13 so you need to set alpha_support=1. This will be fixed in Linux kernel 4.15 (coming in Ubuntu 18.04).
The second issue you describe is bug 1724732. So let's keep this bug just about the first issue.