osc <TAB><TAB>
does not work. It seems autocompletion is broken. In particular,
/usr/share/bash-completion/bash_completion
looks for:
for compfile in "$cmd" "$cmd.bash" "_$cmd"; do

so the installed:
/usr/share/bash-completion/completions/osc.sh
is skipped. The suffix is supposed to be ".bash" or no suffix at all.

If I move it, it's still broken, as the "returned" value is an error from the last command:
test -s /usr/lib/osc/complete   && complete -o default -C /usr/lib/osc/complete osc

If I put 'true' at the end, everything is fine. So the fixed script looks like:
test -z "$BASH_VERSION" && return
complete -o default _nullcommand >/dev/null 2>&1 || return
complete -r _nullcommand >/dev/null 2>&1         || return
test -s /usr/share/osc/complete && complete -o default -C /usr/share/osc/complete osc && return
test -s /usr/lib64/osc/complete && complete -o default -C /usr/lib64/osc/complete osc && return
test -s /usr/lib/osc/complete   && complete -o default -C /usr/lib/osc/complete osc