linux-kernel needs dist-upgrade (again)

[Bonno Bloksma <b.bloksma@tio.nl>]

Hi,

I would like to understand why apt-get upgrade holds backup the upgrade of the Linux kernel. 
---<quote>----------
Calculating upgrade... Done
The following packages have been kept back:
   linux-image-amd64 (4.9+80+deb9u6 => 4.9+80+deb9u7)
---<quote>----------

So I looked at the Debian changelog for the kernel but that states just 
---<quote>----------
linux-latest (80+deb9u7) stretch; urgency=medium

  * Update to 4.9.0-9

 -- Salvatore Bonaccorso <carnil@debian.org>  Fri, 29 Mar 2019 14:41:18 +0100
---<quote>----------

Not much help. :-(
So what is so special about the deb9u6 to debu9u7 upgrade that I need dist-upgrade? What can break during a normal upgrade?

Bonno Bloksma