I don't know how you did format the text to look like it does in your first screenshot.
If I use the paragraph effects defined in Scribus 1.5, I get this:
I just had to check the "Auto-Indent" option.
Looks like what you would expect.
Personally, I'm still using the manual way (defining the indent and adding a tab) but I always do it in a style.
If anything changes in the size of the characters, I can modify the style and the indent gets "automatically" fixed.
It's the way I'm used to do it... but, one day, I will have to get into using the paragraph effects!
Of course, even when using paragraph effects, you should probably define them in paragraph style, so that you can always do changes to the existing text, if you need to do so.