Not a bug with the game per se, but very annoying. Some Bf 109s (mostly Gustavs) have missing weapons.properties entries.
F-4/Z (mg151 gunpod load)
G-1, 2, 3, 4 (recon loads mainly)
G-5, /AS (some recon loads)
G-6 (some cannon/gunpod loads, some recon loads)
G-6 Erla, TallTail (cannon loads and some recon loads)
G-6 Late (many cannon/gunpod loads, some recon loads)
G-6/AS (many cannon/gunpod loads, some recon loads)
G-10 (some cannon/gunpod loads, some recon loads)
G-10 Erla, C3 (some recon loads)
G-14 (some cannon and gunpod loads)
G-14/AS (some cannon/gunpod loads, some recon loads)
K-6 (default loadout has wrong/missing entry)

I can also confirm that the Ju 88 G-6 has no cockpit, and isn't flyable.

java.lang.ClassCastException: com.maddox.il2.objects.air.JU_88G6
at com.maddox.il2.objects.air.CockpitJU_88G6.doFocusEnter(CockpitJU_88G6.java:82)
at com.maddox.il2.objects.air.Cockpit.focusEnter(Cockpit.java:664)
at com.maddox.il2.game.Main3D.setViewInside(Main3D.java:1202)
at com.maddox.il2.game.AircraftHotKeys$74.begin(AircraftHotKeys.java:3040)
at com.maddox.rts.HotKeyCmd.start(HotKeyCmd.java:103)
at com.maddox.rts.HotKeyCmd.exec(HotKeyCmd.java:211)
at com.maddox.rts.HotKeyCmd.exec(HotKeyCmd.java:174)
at com.maddox.il2.gui.GUIMission$4.doAction(GUIMission.java:106)
at com.maddox.rts.MsgAction.doAction(MsgAction.java:36)
at com.maddox.rts.MsgAction.invokeListener(MsgAction.java:152)
at com.maddox.rts.Message._send(Message.java:1217)
at com.maddox.rts.Message.sendToObject(Message.java:1191)
at com.maddox.rts.Message.sendTo(Message.java:1134)
at com.maddox.rts.Message.trySend(Message.java:1115)
at com.maddox.rts.Time.loopMessages(Time.java:180)
at com.maddox.rts.RTSConf.loopMsgs(RTSConf.java:101)
at com.maddox.il2.game.MainWin3D$Background.step(MainWin3D.java:159)
at com.maddox.rts.BackgroundTask.doRun(BackgroundTask.java:167)
at com.maddox.il2.game.MainWin3D.loopApp(MainWin3D.java:108)
at com.maddox.il2.game.Main.exec(Main.java:374)
at com.maddox.il2.game.GameWin3D.main(GameWin3D.java:235)