<s:message>Invalid Mimedir file. Line starting at 12 did not follow iCalendar/vCard conventions</s:message>[LF]
I don’t know what a “Mimedir file” is, but it seems this is an OwnCloud error and not a DAVdroid error, especially when it’s returned on a REPORT addressbook-query request.
@rfc2822, this seems to be correct because I couldn’t reproduce this issue in Android 4.1 emulator. But WAL is not supported on Android 4.0. So, another possible fix is to bump minSdk from 15 to 16 (especially given that ICS has smaller market share than Gingerbread).