Unset builtin not respecting single quotes / doing its own dereferencing

[bitbucket]

   Configuration Information [Automatically generated, do not change]:
   Machine: x86_64
   OS: linux-gnu
   Compiler: gcc
   Compilation CFLAGS: -DPROGRAM='bash' -DCONF_HOSTTYPE='x86_64'
   -DCONF_OSTYPE='linux-gnu' -DCONF_MACHTYPE='x86_64-pc-linux-gnu'
   -DCONF_VENDOR='pc' -DLOCALEDIR='/usr/share/locale' -DPACK$
   uname output: Linux lenovoyoga 4.15.0-43-generic #46-Ubuntu SMP Thu Dec
   6 14:45:28 UTC 2018 x86_64 x86_64 x86_64 GNU/Linux
   Machine Type: x86_64-pc-linux-gnu
   Bash Version: 4.4
   Patch Level: 19
   Release Status: release
   Description:
   When unsetting elements of an associative array, unset does not respect
   the quoting rules, and does its own dereferencing. The behaviour
   appears to be incorrect, or at least undocumented.
   Repeat-By:
   See attached script.

test.sh
Description: application/shellscript