Apparently I went brain dead for a second. So anyway, the aforementioned bug is now fixed. The only bug that I know about (aside from the ones that are in MAME also), is that the title screen of s1945iii isn't 100% correct.
It looks like you're not doing the variable blending effect on the clouds? (each pen blends by a different amount, eg, pen 0 is 0% alpha, pen 1 is 1% alpha, pen 2 is 2% alpha etc. It's documented in MAME)
The most subtle other blending effect is the one that turns the screen slightly blue when you use the bombs in 1945iii etc. (It also causes the screen to tint slightly in Dragon Blaze etc.) I can't tell if you have that covered from your screenshots.
I don't know why the 1945II title screen would look wrong, I don't remember anything special about it.
Also if you want to check your priority implementation some of the later levels in Space Bomber do some fairly funky priority mixing IIRC, likewise, Space Bomber is a good test to make sure that your animated backgrounds work (tilemap base select)