NMI button doesn't place vector on bus
Pressing the NMI button on the board does not assert VPA, nor does it place a vector on the bus. This will essentially cause a random vector to be selected.
Since VPA isn't being used anyway, the hotfix for rev0 will be to cut its trace to 5V and tie it directly to the NMI button. The output is pulled up, so no other modifications are necessary. The level 7 autovector will be used.
For rev1, I will probably have it place a vector on the data bus rather than using VPA. I think this will be a little cleaner, since VPA is basically just a hack so that the CPU can work with 8 bit devices.