SUMMARY
Krita's text editor seems to assume that whatever text is under the cursor represents the "current" settings and will ignore any attempted changes to settings that match the text under the cursor, even if highlighted text includes text with different fonts and sizes. Note that this does not happen with color.

STEPS TO REPRODUCE
1. Make new text with the text tool
2. In the text box, make the right half of the text a different size/font
3. Highlight text containing characters of both sizes/fonts, so that the cursor ends up on the right half
4. Attempt to change all the text to the size/font of text on the right half
(alternatively, highlight right to left and attempt to change back to the original size/font)

OBSERVED RESULT
Size/font in the dropdown menu is already on the setting of whatever text is under the text cursor (regardless of highlighted text), and re-selecting it has no effect on highlighted text.

EXPECTED RESULT
In any other text editor, the contents of the dropdown become blank if highlighted text includes different values for that setting, and any selection made from the dropdown applies it to all of the highlighted text.

SOFTWARE/OS VERSIONS
Windows: 10