The wikidata property Baltisches Biographisches Lexikon digital ID - https://www.wikidata.org/wiki/Property:P2580 - takes a string value and uses a formatter URL to enable users to click through to the BBL record for the item.

Some BBL URLs have trailing spaces. So, for example:

*http://www.bbl-digital.de/eintrag/Beggrow-Hartmann-Olga-1862-1922%20/ -> works
*http://www.bbl-digital.de/eintrag/Beggrow-Hartmann-Olga-1862-1922/ -> does not work

However the UI appears to prevent us from entering "Beggrow-Hartmann-Olga-1862-1922 " as the P2580 value.

Given the current formatter URL of http://www.bbl-digital.de/eintrag/$1/ and the observation that http://www.bbl-digital.de/eintrag/Beggrow-Hartmann-Olga-1862-1922%20/ is the desired output URL, then:

Steps to Reproduce

1. Go to https://www.wikidata.org/wiki/Q36538626
2. Click edit on the Baltisches Biographisches Lexikon digital ID
3. Enter "Beggrow-Hartmann-Olga-1862-1922 " (without the quote marks)
4. Note that the publish button is greyed out

Expected result:
the publish button is not greyed out; publishing the entered string saves it and the value saved is "Beggrow-Hartmann-Olga-1862-1922 " (without quote marks)

Actual result:
the publish button is greyed out and it is not possible to save the desired value.

Note, finally, that entering
Beggrow-Hartmann-Olga-1862-1922%20
yields an output of
Beggrow-Hartmann-Olga-1862-1922%2520