`set completion-ignore-case on' does not work well for the first word on command line

[Jian Wang]

When using Bash, I often turn on the `completion-ignore-case' option of
readline. It works fine for most cases but sometimes it does not work as
expected when completing the first word on the command line. For example,
there is a bash script ~/MyDir/Foo.sh, on command line, when I input ~/my
and then press TAB, the word is completed as ~/myDir . Is that a bug?