I thought I found a workaround, but instead I think I may have found yet another bug. Unbelievable.
Workaround: Use AudioSuite Normalize using PEAK setting. This should make sure nothing goes out over 0DBFS. An extra step, but fine for me. Indeed, seems to work and proper waveform is recovered and displayed!
Now, accidentally, I tried to normalise again to 0dB PEAK, but strangely enough, Pro Tools shrunk the audio even further! This should not happen, PEAK should stay PEAK! I'll try to attach a screenshot.
Another bug, right?