Sorry Seppel but I can't confirm the issues of FMB as I have used it a lot , i build my 4.3 starting from a 4.12.2 stock installation and adding all BAT modules....
Are you sure you have the correct bldconf.ini file entries?
[builder_plugins]
(builder.PlMapLoad)
(builder.PlMission)
(builder.PlMisAir,sectFile=com/maddox/il2/objects/air.ini)
(builder.PlMisChief,sectFile=com/maddox/il2/objects/chief.ini)
(builder.PlMisStatic,sectFile=com/maddox/il2/objects/stationary.ini)
(builder.PlMisRocket,sectFile=com/maddox/il2/objects/rockets.ini)
(builder.PlMisHouse,sectFile=com/maddox/il2/objects/static.ini)
(builder.PlMisTarget)
(builder.PlMisBrief)
(builder.PlMisBorn)
(builder.PlMisStaticCamera)
(builder.PlMisDestruction)
(builder.PlMisFront)
(builder.PlMisTrigger)
[builder config]
bShowGrid true
bShowName false
bViewRunaway true
bShowTime false
bShowArmy [3,true,true,true]
iLightLand 255
iconSize 32
bViewBridge true
bAnimateCamera true
bActorOnLand true
bSaveViewHLand true
bShowLandscape true
iLightDestruction 91
iWaterLevel 191
defFullDX 32.0
defFullDY 24.0