Hi Fud. I don't own either of these lenses but I do agree that they do not have a reputation for creating CA, therefore the translucent mirror on the A77 is a reasonable possibility. I own an A77 and I have had CA caused by some lenses, but I know what lenses they are and under what circumstances they cause it. Even my better lenses will occasionally cause CA but generally seen only when I pixel peep. I have never heard anyone complain about CA from the translucent mirror, only from lenses.
The usual definition of Chromatic Aberration is as stated here here.
That said, I hardly think that the very thin and soft mirror on SLTs could could cause CA. I suppose it could be possible, but very unlikely.
Sony A7, A850, A77, A700 || Sony>> 70-300G, 28-75 f2.8 SAM, 16-80CZ, 50 f1.4, FE 28-70 OSS, FE 24-70CZ f4 OSS, LA-EA4 || Minolta>> 300 f4 G HS, 200 f2.8 G HS, 100 f2.8 (D) Macro, 50 f1.7, 28 f2.8, 28-135 f4-4.5, 70-210 f4, 500 f8 Reflex, TC x 1.4 HS, TC x 2 HS. || Sigma 21-35 f3.5-4.2. || Tamron SP 24-135.