The blue highlighted text background for signs is gone

Ever since 24w33a, the highlighted text for sign background has vanished. It still appears is all other textboxes except for the sign gui.

(the blue highlighted text is 1.21.1 and the white text is 24w33a/24w34a)

Steps to reproduce:

1. Open a sign gui
2. Highlight text written on the sign
   → The text highlight background doesn't appear