This has been going on with the B-29 since I can remember and just happened to notice it on the Betty as well:
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The lead drone is transparent inside. If you zoom the view close enough, the inside appears but no pilots are seen.
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The drones appear normally until one becomes the lead and then becomes transparent.
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I saw the same issue in a screen shot someone posted, so I'm not the only one seeing this.
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All the other bombers are rendered normally. The Betty pics were from today and the B-17 from yesterday.
The B-29 pic was taken from the last tour - the most recent I could get.
Maybe something to do with the 2048 textures in the newer cockpits?