apt-get not installing but aptitude does?

[Bob Proulx <bob@proulx.com>]

Hello apt-get maintainers,

  # apt-get dist-upgrade
  Reading package lists... Done
  Building dependency tree       
  Reading state information... Done
  Calculating upgrade... Done
  The following packages have been kept back:
    libdb-dev
  0 upgraded, 0 newly installed, 0 to remove and 1 not upgraded.

But aptitude is okay with the upgrade.

  # aptitude safe-upgrade
  Resolving dependencies...                
  The following NEW packages will be installed:
    libdb5.3-dev{a} 
  The following packages will be REMOVED:
    libdb5.1-dev{u} 
  The following packages will be upgraded:
    libdb-dev 
  1 packages upgraded, 1 newly installed, 1 to remove and 0 not upgraded.
  Need to get 719 kB of archives. After unpacking 301 kB will be used.
  Do you want to continue? [Y/n/?]

Explicitly installing libdb-dev works of course.

  # apt-get install libdb-dev
  Reading package lists... Done
  Building dependency tree       
  Reading state information... Done
  The following extra packages will be installed:
    libdb5.3-dev
  Suggested packages:
    db5.3-doc
  The following packages will be REMOVED:
    libdb5.1-dev
  The following NEW packages will be installed:
    libdb5.3-dev
  The following packages will be upgraded:
    libdb-dev
  1 upgraded, 1 newly installed, 1 to remove and 0 not upgraded.
  Need to get 719 kB of archives.
  After this operation, 301 kB of additional disk space will be used.
  Do you want to continue? [Y/n]

Turning on debug shows:

  # apt-get -o Debug::pkgProblemResolver=yes dist-upgrade
  Reading package lists... Done
  Building dependency tree       
  Reading state information... Done
  Calculating upgrade... Starting pkgProblemResolver with broken count: 2
  Starting 2 pkgProblemResolver with broken count: 2
  Investigating (0) libdb-dev [ amd64 ] < 5.1.7 -> 5.3.0 > ( libdevel )
  Broken libdb-dev:amd64 Conflicts on libdb5.1-dev [ amd64 ] < 5.1.29-7 > ( libdevel )
    Considering libdb5.1-dev:amd64 -1 as a solution to libdb-dev:amd64 -1
    Holding Back libdb-dev:amd64 rather than change libdb5.1-dev:amd64
  Investigating (0) libdb5.3-dev [ amd64 ] < none -> 5.3.28-3 > ( libdevel )
  Broken libdb5.3-dev:amd64 Conflicts on libdb5.1-dev [ amd64 ] < 5.1.29-7 > ( libdevel )
    Considering libdb5.1-dev:amd64 -1 as a solution to libdb5.3-dev:amd64 -1
    Holding Back libdb5.3-dev:amd64 rather than change libdb5.1-dev:amd64
   Try to Re-Instate (1) libdb-dev:amd64
  Done
  Done
  Starting pkgProblemResolver with broken count: 0
  Starting 2 pkgProblemResolver with broken count: 0
  Done
  The following packages have been kept back:
    libdb-dev
  0 upgraded, 0 newly installed, 0 to remove and 1 not upgraded.

I don't understand what the debug output is saying.  Why won't this
package upgrade normally?

Thanks,
Bob

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