Listboxes in Base forms are greyed out and no longer function. Information previously entered displays, but is likewise greyed out and cannot be modified. This affects Manjaro Linux, and possibly Arch and other Arch-based distros. It does not affect Fedora. I discovered the issue when switching distros, so it could possibly affect earlier versions of LibreOffice Base as well.
@Basil : this is a distrib-specific problem, as you have said yourself, because it works on Fedora, so this is the wrong place to report this bug. Please open a bug report on the specific distro-provided list (assuming there is one). If the problem is one that is applicable to version 5.0.6.3 irrespective of OS, then do not hesitate to re-open here. Closing as NOTOURBUG.