"stty -a" on both systems prints:
speed 38400 baud; rows 57; columns 237; line = 0;
intr = ^C; quit = ^\; erase = ^H; kill = ^U; eof = ^D; eol = <undef>; eol2 = <undef>; swtch = <undef>; start = ^Q; stop = ^S; susp = ^Z; rprnt = ^R; werase = ^W; lnext = ^V; flush = ^O; min = 1; time = 0;
-parenb -parodd cs8 -hupcl -cstopb cread -clocal -crtscts
-ignbrk brkint -ignpar -parmrk -inpck -istrip -inlcr -igncr icrnl -ixon -ixoff -iuclc -ixany imaxbel -iutf8
opost -olcuc -ocrnl onlcr -onocr -onlret -ofill -ofdel nl0 cr0 tab0 bs0 vt0 ff0
isig icanon iexten echo echoe echok -echonl -noflsh -xcase -tostop -echoprt echoctl echoke
(The Debian 6.0.10 version had "ignpar", but changing it to match the Linux Mint 17.2 system didn't change the behavior.)
readline is included in bash-4.4-beta.tar.gz, so they're both using the same version.
On both systems, I built bash using:
./configure --prefix=...
make
make install
One possibly relevant observation: the output of "ldd" on the executables differs. On Debian 6.0.10, it's:
$ ldd /usr/local/bin/bash
linux-vdso.so.1 => (0x00007ffe2e775000)
libncurses.so.5 => /lib/libncurses.so.5 (0x00007f730c0ae000)
libdl.so.2 => /lib/libdl.so.2 (0x00007f730beaa000)
libc.so.6 => /lib/libc.so.6 (0x00007f730bb40000)
/lib64/ld-linux-x86-64.so.2 (0x00007f730c318000)
On Linux Mint 17.2, it's:
$ ldd /usr/local/bin/bash
linux-vdso.so.1 => (0x00007ffddfd8b000)
libtinfo.so.5 => /lib/x86_64-linux-gnu/libtinfo.so.5 (0x00007fd51ce92000)
libdl.so.2 => /lib/x86_64-linux-gnu/libdl.so.2 (0x00007fd51cc8e000)
libc.so.6 => /lib/x86_64-linux-gnu/libc.so.6 (0x00007fd51c8c8000)
/lib64/ld-linux-x86-64.so.2 (0x00007fd51d0e3000)
But I see the same difference on /bin/bash (4.1.5 on the Debian system, 4.3.11 on the Linux Mint system).