Problem: Characters with two pronunciations/meanings pronounced and written (in pinyin) differently.
I had a hard time searching the discussion, so this may have already been raised as an issue. If not, here goes: I've noticed that characters that have two (or more) pronunciations, particularly two different tones, often have discrepancies in pronunciation and pinyin in Duolingo. For instance, the pinyin for 假 is written as jià (fourth tone) in the Chinese course; however, it is pronounced as jiǎ (third tone) in the same course. Both are correct pronunciations; however, they do not seem to mean the same thing. Has anyone else noticed this? Is there a time line to fix this? Again, this is not an isolated incident. My wife and I have noticed quite a few of these problems.
This also happens in the Japanese course. Unfortunately, the way in which Duolingo courses are designed does not allow for multiple readings to be taught, as each character is assigned a single pronunciation for testing, so I don't imagine it will get fixed any time soon.
In addition, sometimes the TTS uses a reading of a character when it is in isolation that does not occur in the course (as in your '假' example). This problem probably could be fixed without any drastic changes, although it wouldn't help where characters with multiple readings do occur (e.g. jiao4/jue2, etc.)
You might find this website helpful: https://www.mdbg.net/chinese/dictionary?page=worddict&wdrst=0&wdqb=%E5%81%87
It is a common thing in Chinese to have characters that have different meanings when pronounced differently. It's similar to how play has all those different meanings to it, the difference is just that it is pronounced differently.