Why m4a encoding has become worse?

[racemus]

Hi

I found out that the old 6.1.2 version did m4a encoding better than the current version. I tried it on the same book with the same quality settings:

With version 6.1.2, I got a 147 MB file, and with the current version, the file size is 297 MB. They sound the same, but the spectrum analysis of the file from version 6.1.2 is even slightly better.
File from 6.1.2

File from 6.5.2

What's wrong?

[yermak]

vs current 6.5.2?

[racemus]

@yermak, yes, by current version I mean 6.5.2