Hi Antonio!
I'm using the apt installed version of XBoard, 4.9.1-1 amd64, in
Debian GNU/Linux 10 (buster) x86_64 (Kernel: 4.9.0-9-amd64).
I also use the apt installed version of GNU Chess, 6.2.5-1 amd64. The
previous version I tried, 6.2.4, I compiled from source
(
https://ftp.gnu.org/gnu/chess/) and it works as expected without this
bug (ie, the 'White (1) : ' prompt does not appear in UCI mode).
Ryan