I haven't dug into this (maybe Serge can explain in more detail), but I think this comment (Modules/readline.c in python sources) gives a general overview of the problem. Ignore the "On OSX" part, the same should apply to any OS.
* It is possible to link the readline module to the readline
* emulation library of editline/libedit.
Is this a packaging issue?
There are good reasons to use libedit as a gnu readline drop in
replacement. The most important one is certainly saner licensing state
as gnu readline is GPLv3 and it makes it incompatible with at least
GPLv2 users (there are users that pick old gnureadline GPLv2 around).
If there are known incompatibilities, I think (not speaking on behalf of
Christos) it would be best to contribute patches with rationale. Generic
call for compatibility might not work well.
Well, I was hoping that for someone intimately familiar with libedit (i.e., Christos) the difference in behavior would be obvious from just looking at that patch. But, of course, I can't make anyone do anything (nor I want to do that), so if fixing/figuring that out requires more time than you're willing to devote to that right now, then yes, I guess it means I or someone else will have to dive in and figure out what's wrong (eventually).