Weird ; as I said I'm not really sure what the pattern is, I had a little play with my Views -> [Fields] settings...
(the NSQL in my lookup is much the same as yours, on Oracle and replacing chr(10) with <br> in the string - maybe I have one less to_char in my statement as I don't think you need the outer one?)
If I set the "Display Type" to pull-down and check "Enter Once" - I get line breaks OK on my object page
If I set the "Display Type" to pull-down and un-check "Enter Once" - I get a single edittable line with <br> visible in the text (i.e. wrong)
If I set the "Display Type" to browse and un-check "Enter Once" - I get a truncated edittable line with <br> visible in the text (i.e. very wrong)
If I set the "Display Type" to browse and check "Enter Once" - I get a single un-edittable line with <br> visible in the text (i.e. wrong ; the same as your last screenshot)
(this is in an older 13.x version of the UI though, that might make a difference?)
--
If you "hard code" some text with <br> in it in your lookup (just as a test) what happens?
eg
SELECT 'aaa<br>bbb<br>ccc<br>' as COMENTARIO
from niku.odf_ca_inv
...