We tested this with identical settings (German DD+ and Polish AC3 language, no compression) and couldn't observe any problems.
Playback with a Sony, a Samsung and a Panasonic player, over a Denon recevier. PowerDVD 16 as well.
Both audio tracks audible in all test cases.
I suggest, you should try to test your result on different equipment or a different receiver (or if possible have your BD player decode the sound, if it supports that), to find the cause.
Alternatively test the disc with PowerDVD.