MY FIX:
-I dropped the source clip in MPEG Streamclip.
-I set I/O’s and re-export.
In my options:
-I changed the frame size. (in my strange and aggravating dilemma from 1248 x 702 to 1280 x 720)
-then I exported at full quality, Apple HDV 720p24 compression.
I know now what went wrong, but this fix is my answer to not re-compressing my 70+ hours of footage…once again, Mr. MPEG Streamclip has come through for me big.