\allowdisplaybreaks does not work anymore if empheq is loaded

Question

I'm using the package mathtools using the option showonlyrefs. This works fine, however some equation numbers are skipped. If I understood the manual correctly I need to load empheq to fix this. This works!

The problem now is that without empheq \allowdisplaybreaks works fine, but the equation numbering goes wrong, but with empheq the \allowdisplaybreaks seems to stop working (this is a command from amsmath).

Is this a common problem? I can't seem to find anything about it. How can I solve this?

Edit: I have finally found the time to make a MWE. See below.

\documentclass[a4paper,10pt, leqno, final, twoside]{scrbook}
\usepackage{amsmath}
\usepackage[overload, ntheorem]{empheq}
\usepackage[amsmath, thmmarks]{ntheorem}
\allowdisplaybreaks[4]
\usepackage{mathtools}
\mathtoolsset{showonlyrefs}
\mathtoolsset{showonlyrefs,showmanualtags}
\newtagform{brackets}{[}{]}
\usetagform{brackets}
\usepackage{blindtext}

\begin{document}

\blindtext[3]
\begin{align}
  A &= A\\
  &= A\\
  &= A\\
  &= A\\
  &= A\\
  &= A\\
  &= A\\
  &= A\\
  &= A\\
  &= A\\
  &= A\\
  &= A\\
  &= A\\
  &= A\\
  &= A\\
  &= A\\
  &= A
\end{align}

\end{document}

Answer 1

Drop the overload option for the empheq package. You then can't use the short form for emphasized equations. See Section 2.2.2 of the package manual.