With a suggestion from POTN'r apersson580, I believe this problem is solved. Use FEL to set your flash exposures with the 70D. It works like a charm. See: https://photography-on-the.net …read.php?t=1442842&page=9
Might be a workaround, but I would hardly call that solution being "solved". It would be a major PIA to have to use FEL every time you use bounce flash, which for me is quite often.