pinentry-qt hangs when pressing Menu key then Esc

A Debian user reported (bug #303508) the following, which I can confirm:

To reproduce this bug, you must have a keyboard with a Menu key (or some
other key, I suppose) that is mapped to open a context menu.  I believe
this is the default mapping for this key, if you have it.  (On my
keyboard, the Menu key is between the right Logo key and the right Ctrl
key.)

1. from a terminal, run pinentry-qt
2. type getpin<Enter>  (a pin entry dialog box should appear)
3. in the dialog box, press the Menu key  (a context menu should appear)
4. press Esc

At this point, the dialog box will dissappear, but no response will be
returned to the terminal.  (If you omit step 3, you will get the
response "ERR 111 canceled", which is what we want.)

This bug manifested itself to me as kmail hanging after I accidentally
mistyped my passphrase (by hitting the Menu key instead of Shift, which
is right above it) and then hitting Esc to get a fresh start.  At this
point the context menu was showing, and it hung as described, and kmail
hung too because it was still waiting for a response.

(Note that if you get the context menu for the line edit using the right
mouse button instead of the Menu key, this bug does not appear.)

Also, other apps that use a line edit do not behave this way; for
example, to see the expected behaviour, do this:
1. run kdialog --inputbox test
2. follow steps 3-4 above