Using the text view rule doesn't show any text when expanded, but the expanded panel does seem like it knows there should be text there as i'm able to select the correct amount of characters in it using the mouse and manually counting.
I'm also not sure if this might be theme related in some way (like the characters having the same color as the background), but changing the theme didn't help.

Another issue is when you have the text view expanded, then edit the expression. Assuming const char *String = "hi there", then:
text(String) will show there are 8 characters (by counting how many characters can be selected)
then changing the expression to text(String, size=4) will truncate it down to 4 selectable characters
then changing the expression back to text(String) will not revert reset the size, and the panel will still show only 4 selectable characters (again, using the mouse to select text and counting how many characters the selection increments by).
Closing the expanded view and expanding again fixes/resets the count.

Also, while on the topic of the text view, the button to pull out as new tab, since i can't check atm how it works when there is a bunch of text in multiple lines and whether it moves as to not obstruct the text, it still feels like it's a bit too close to the content in the default position. Could this button be moved, or the panel layout a bit reorganized, so the button never obstructs any of the text lines?