history-incremental-search-backward weird behavior for multiline commands in 5.0.x

[Augie Fackler <raf@xxxxxxxxxxx>]

I upgraded my work machine from zsh 4.3.17 to zsh 5.0.5 (also tested 5.0.2
first, as that was what was in apt), and now
history-incremental-search-backward doesn't work correctly for multiline
history entries loaded from a history file on disk. As an example:

$ echo foo \
>  bar
foo bar
$ ^R bar
# finds the full command

but then in a new shell:
$ ^R bar
# finds only the word bar, not the full echo command.

This works fine in zsh 4.3.17 and zsh 4.3.11 (I get the same behavior even
if the history entry was loaded from a file).

Am I missing something obvious? setopt hist_lex_words didn't make a
difference, and I tried turning off hist_save_no_dups and
inc_append_history.

Thanks!