Two different core files generated at different occasions of application crash

Question

I wanted my C++ application to produce core dumps when it crashed, so I followed this advice: https://stackoverflow.com/questions/2065912/core-dumped-but-core-file-is-not-in-the-current-directory

Sometimes, when it crashes it produces a single core file in the directory when it was started (e.g. my home directory), and sometimes it creates a file named _usr_bin_<app_nam>.1000.crash in /var/crash. It looks like two different mechanisms were responsible for creation of these files.

The application and its debug symbols is installed from a debian package to /usr/bin (it is build as RELEASE_WITH_DEBUG_INFO).

Here is some of the relevant configuration:

$ cat /proc/sys/kernel/core_pattern
|/usr/share/apport/apport %p %s %c %d %P %E

$ cat /etc/apport/crashdb.conf
[...]
databases = {
    'ubuntu': {
        'impl': 'launchpad',
        'bug_pattern_url': 'http://people.canonical.com/~ubuntu-archive/bugpatterns/bugpatterns.xml',
        'dupdb_url': 'http://people.canonical.com/~ubuntu-archive/apport-duplicates',
        'distro': 'ubuntu',
#        'problem_types': ['Bug', 'Package'],
        'escalation_tag': 'bugpattern-needed',
        'escalated_tag': 'bugpattern-written',
    },
[...]
}

$ ulimit -a
core file size          (blocks, -c) unlimited
data seg size           (kbytes, -d) unlimited
scheduling priority             (-e) 0
file size               (blocks, -f) unlimited
pending signals                 (-i) 63058
max locked memory       (kbytes, -l) 64
max memory size         (kbytes, -m) unlimited
open files                      (-n) 1024
pipe size            (512 bytes, -p) 8
POSIX message queues     (bytes, -q) 819200
real-time priority              (-r) 0
stack size              (kbytes, -s) 8192
cpu time               (seconds, -t) unlimited
max user processes              (-u) 63058
virtual memory          (kbytes, -v) unlimited
file locks                      (-x) unlimited

The # in the crashdb.conf file was inserted to enable apport , as recommended here: https://wiki.ubuntu.com/Apport

Also, when I am opening the core file from my home dir in gdb, it says: BFD: Warning: core is truncated: expected core file size >= 2697007104, found: 2147479552. and it failed to read a valid object from the memory. It should not be a problem with free disk space.

What is exactly the reason of producing two types of core dumps?