It is not easy to explain or reproduce it but I have the feeling it has something to do with different formating's in one and the same text. I don't think that the text editor is able to handle that correct or "read" correct the information out of a marked Text. E.g. if I have a text with multiple Text fonts and mark this text the text editor should give me the Text Font Info "Varies" but only one Textfont is shown. The same story with multiple Text hight's ....
I reported a "Bug" because it seams to me not right that the "Text Contents" includes Formating Infos like \H1; what means the Hight of the Text is fix. But on the other Hand I have at the same time the Info in the Property Editor that this text is not "Simple" what means the text is not fix ....Anywhere - I been told that this is desired on that way.
Funny is - if I remove the H1 tag I can easily change my Text Hight in the Property Editor ... or maybe not funny
Here are two dxf for testing. Just select the text and change only the Hight in the Property editor and look then what happens with the text in your drawing ....
... this one is really funny
To make a long story short: What ever I do with text in QCAD it's like walking on eggs for me. More luck than plan