OpenPGP breaks for newline in html-formatted signature

Environment: Thunderbird for Android: 24.0 OpenKeychain: 6.0.4 (60400) Android Version: 17 Andorid Build: CP3A.261005.002.A1 When sending a PGP/MIME-signed message from Thunderbird for Android, the OpenPGP signature becomes invalid when an HTML-formatted signature contains markup that enforces line breaks. A plain newline in the HTML source does not create a visible line break, as expected because HTML collapses whitespace. However, adding any of the following causes the signature to become invalid: <br> <div></div> <div>&nbsp;</div> The first and second are used to create a normal line break and the third is used to create an empty spacing line. Inline HTML formatting, such as <strong> or <a>, does not cause the problem. Expected result: HTML line-break elements should be included in the content covered by the OpenPGP signature, and the signature should remain valid. Actual result: The message is sent successfully, but the received OpenPGP signature cannot be verified whenever the HTML signature contains markup for a line break or empty spacing line. The issue does not occur when the signature contains only text and inline formatting. Raw .eml samples can be provided if needed.