So, if you are uploading Media Comments and Text Comments in the "Assignment Comments" section of Speed Grader, make sure you upload each individually as two (2) separate comments. I found out that the students won't see the text if it is coupled with a media comment in the same post.
For example... I upload a screencast of grading a student's assignment, attached to the assignment itself with text above....
However, when the student goes in to Canvas to look at their assignment, all that she or he will see is:
...or...
The only workaround is to upload/publish media comments and text-only comments separately, otherwise, the media comment is all that will show.
Canvas does the same thing if I record audio or video directly via Flash.
John, I heard back from Canvas support. Here is what they indicated:
"I understand that you've discovered that, when adding media comments with additional text on the comment, students are unable to see the full comment. Thank you for reporting this! I was able to confirm this behavior when testing it on my sandbox, and discovered our engineering team has a project related to this behavior. Because of this, I am going to attach your case to their project tracker so they can use your case as a reference point and alert you of any changes they make regarding it."
So it sounds as though the engineers are working on it, but it is good to know that until this is taken care of the text and media comments need to be added separately, as you outlined.