autopkgtest dependency irritiation

[Ole Streicher <olebole@debian.org>]

Hi,

I have a rather difficult set of packages that need to be updated
somehow together. I puzzled out the breakages and declared them. Namely,
this is the binary package starlink-utils-java, that breaks the old
version of starlink-ttools-java. This is properly mentioned in
d/control:

Package: starlink-util-java
Architecture: all
Depends: ${java:Depends},
         ${misc:Depends}
Breaks: starlink-topcat-java (<< 4.8~),
        starlink-ttools-java (<< 3.4~),
        starlink-vo-java (<< 0.2+2019.09.18~),

When I however look into a CI log, I see a failure in combination of
these two packages:

https://ci.debian.net/data/autopkgtest/testing/armhf/s/starjava-ttools/10234315/log.gz

The failure is in principle OK, however the test is just useless since
it tests a combination that is broken. The log tells me the following
about it:

--------------------------------------8<-------------------------------------------
Correcting dependencies...Starting pkgProblemResolver with broken count: 1
Starting 2 pkgProblemResolver with broken count: 1
Investigating (0) autopkgtest-satdep:armhf < 0 @iU mK Nb Ib >
Broken autopkgtest-satdep:armhf Depends on starlink-ttools-java:armhf < none @un H >
  Considering starlink-ttools-java:armhf 1 as a solution to autopkgtest-satdep:armhf -2
  Removing autopkgtest-satdep:armhf rather than change starlink-ttools-java:armhf
Done
 Done
Starting pkgProblemResolver with broken count: 0
Starting 2 pkgProblemResolver with broken count: 0
Done
The following additional packages will be installed:
  ca-certificates openssl
The following packages will be REMOVED:
  autopkgtest-satdep
The following NEW packages will be installed:
  ca-certificates openssl
0 upgraded, 2 newly installed, 1 to remove and 0 not upgraded.
1 not fully installed or removed.
Need to get 983 kB of archives.
--------------------------------------8<-------------------------------------------

which I do not understand. Why does the resolver remove the helper
package instead of giving up? How can I avoud this, and (since this is
listed as a cause preventing migration) and let my package migrate?

And why does this happen only on armhf?

Cheers

Ole