This same bug was present several years ago, and subsequently fixed. Now it's back.
DNxHD MOV files are exported with the "PC" video level metadata flag. This equates to RGB/FULL color levels.
As recently as 14.3.2, it was correctly exporting with the "TV" level flag. This equates to Rec709/LEGAL video levels.
The two ffmpeg outputs shown below come from files exported with the same settings in two different versions of PPro.
Premiere Pro 14.3.2:
Stream #0:0(eng): Video: dnxhd (DNXHD) (AVdn / 0x6E645641), yuv422p(tv, bt709/unknown/unknown, top coded first (swapped)), 1920x1080, 145344 kb/s, SAR 1:1 DAR 16:9, 29.97 fps, 29.97 tbr, 30k tbn, 30k tbc (default)
Premiere Pro 14.8.0:
Stream #0:0(eng): Video: dnxhd (DNXHD) (AVdn / 0x6E645641), yuv422p(pc, bt709/unknown/unknown, top coded first (swapped)), 1920x1080, 145344 kb/s, SAR 1:1 DAR 16:9, 29.97 fps, 29.97 tbr, 30k tbn, 30k tbc (default)
I've stepped through the releases and it appears this bug was introduced (re-introduced...) at PPro version 14.6.
That surprised me, as I was expecting the introduction of the HDR workflow (14.4) to be the point at which it started. Not so.
The feedback I received from one of our Devs is that we always export full range. There was a bug that was fixed in 14.6, that we were incorrectly stamping an Avid specific metadata flag as 'limited range' even though the stream was in fact full. We fixed that incorrect flag in the QuickTime wrapper, in PPro 14.6.
If this was intentional on the part of Adobe, is there a reason this change is not in the release notes?
Encoders that utilize the QuickTime libraries offer TV/PC as a choice (TV=709, PC=RGB):
Could Adobe offer this choice as well? We want this flag included because we are a broadcast station, and we want to be consistent across numerous pieces of software (more than just Adobe CC products) - 709 across the board for HD content.
XDCAM export still uses the TV flag in PPro 14.6+. We use both of these codecs, so, again, we want consistency with this flag (709 across the board).
XDCAM Premiere Pro 14.6:
Stream #0:0: Video: mpeg2video (4:2:2), yuv422p(tv, unknown/bt709/bt709, top first), 1920x1080 [SAR 1:1 DAR 16:9], 50000 kb/s, 29.97 fps, 29.97 tbr, 29.97 tbn, 59.94 tbc
Adobe now says they will fix this, reversing the previous "fix" from 14.6-on:
...according to the engineer the behavior that you posted about should be fixed in the next update, which is due out shortly. I can't provide a specific date at this time.
What will be fixed:
The "PC" flag in 14.8 DNxHD MOV exports will revert to the previous behavior, i.e. "TV" as in earlier versions.
Appears to have been fixed as of 15.2 (possibly in 15.1 as well, which I didn't test).