I know this seems like such an obvious question, but I'm going to ask it anyway. Have you actually created the second block in the Diplomacy research field through the player entity, Window, and Brush files? If so, can I see those files?
I'd really love to know what window file you believe contains block information. Brush files would have no bearing on this. And of course we have added a second block to the player entity file.
Here is the section in ResearchScreen.window for the diplomacyContentWindow. I don't see anything in regards to blocks outside of the player files. Additionally, this section looks identical to the Combat and NonCombat portions.
diplomacyContentWindow
blockWindowSharedDef
titleArea [18, 20, 200, 30]
titleFontId "Label"
buttonTopLeftOffset [184, 8]
buttonSize [50 , 36]
buttonSpacing [14, 10]
buttonSpecificDef
barsOffsetFromTop 4
barsWidthModifier -5
backdrop "ResearchWindowButtonBackdrop"
overlay ""
maxLevelOverlay "ResearchWindowButtonMaxLevelOverlay"
isBackdropStretched TRUE