Text inserted in wrong place when replying (including quoted text) to message from AOL Android

When replying to an email sent by AOL Android that is itself a reply, the text of the reply I type, followed by the prefix or header (depending on the "Reply quoting style" setting) are not placed before the quoted AOL message. Instead, they are inserted inside the quoted AOL message after its first reply header.

Expected behavior

Text of reply, followed by the prefix/header created by K9, precede the entire quoted message.

Actual behavior

Text of reply, followed by the prefix/header created by K9, are inserted into the quoted message after the first reply header it contains.

Steps to reproduce

1. Send a message to an AOL email account.
2. Using the AOL Android app, reply to the message.
3. Using the K9 Android app, reply to the reply. Observe that in this reply, K9 inserted the reply and header after the header contained in the AOL reply, not before the AOL reply.

The following (a decoding of the quoted-printable content sent by K9) shows the result of this test:

• john@fastmail.net SENDS TO bruce@aol.com
• bruce@aol.com (using AOL Android) REPLIES TO john@fastmail.net (at November 5, 2019 5:06:07 PM EST)
• john@fastmail.net (using K9) REPLIES TO bruce@aol.com

The first reply, using the AOL Android app.

---

On Tuesday, November 5, 2019 John A <john@fastmail.net> wrote:

The second reply, using K9.

---

From: Bruce B <bruce@aol.com>
Sent: November 5, 2019 5:06:07 PM EST
To: john@fastmail.net
Subject: RE: Test message

This is the original message.

Environment

K-9 Mail version: 5.600

Android version: 8.0.0

Account type (IMAP, POP3, WebDAV/Exchange): IMAP

Example AOL mailers:

• X-Mailer: WebService/1.1.13913 aolandroid Mozilla/5.0 ...
• X-Mailer: WebService/1.1.14680 aolandroid Mozilla/5.0 ...

No source file or test is named. Start by reproducing the AOL Android reply case through K-9's reply and quoting flow, then trace where the reply text and header are inserted relative to the quoted message. Done means the reply text and K-9 header precede the entire quoted AOL message under both quoting-style settings.