This only happens about 1 in 7 clicks when I have my 465 on my 50D's shoe in ETTL mode. I see the flash fire (maybe only the preflash) but the image is dark like the flash didn't fire. EXIF says it did. Camera is set to M mode. My 430EX doesn't do it so it must be the flash. Doesn't happen if I have the 465 in manual mode which is maybe why I only just noticed it. Any ideas other than it's broken?