FWIW, I'm still seeing these errors on OS X (10.11.5 with ActiveTcl 8.5.18) using 2.7.12rc1, 3.5.2rc1, and top-of-trunk 3.6.0.  They do not occur on the same platform when using 2.7.11 or 3.5.1.

For example:
$ /usr/local/bin/python2.7
Python 2.7.12rc1 (v2.7.12rc1:13912cd1e7e8, Jun 11 2016, 15:32:34)
[GCC 4.2.1 (Apple Inc. build 5666) (dot 3)] on darwin [...]
$ /usr/local/bin/python2.7 -m test.regrtest -ugui -j3 test_idle
can't invoke "event" command:  application has been destroyed
    while executing
"event generate $w <<ThemeChanged>>"
    (procedure "ttk::ThemeChanged" line 6)
    invoked from within
"ttk::ThemeChanged"
can't invoke "event" command:  application has been destroyed
    while executing
"event generate $w <<ThemeChanged>>"
    (procedure "ttk::ThemeChanged" line 6)
    invoked from within
"ttk::ThemeChanged"
[1/1] test_idle
1 test OK.

$ /usr/local/bin/python3.5
Python 3.5.2rc1 (v3.5.2rc1:68feec6488b2, Jun 11 2016, 21:59:53)
[GCC 4.2.1 (Apple Inc. build 5666) (dot 3)] on darwin [...]
$ /usr/local/bin/python3.5 -m test.regrtest -ugui test_idle
[1/1] test_idle
can't invoke "event" command:  application has been destroyed
    while executing
"event generate $w <<ThemeChanged>>"
    (procedure "ttk::ThemeChanged" line 6)
    invoked from within
"ttk::ThemeChanged"
1 test OK.

$ ./bin/python3.6
Python 3.6.0a2+ (default, Jun 19 2016, 13:19:06)
[GCC 4.2.1 Compatible Apple LLVM 7.3.0 (clang-703.0.29)] on darwin [...]
$ ./bin/python3.6 -m test -ugui -j3 test_idle
Run tests in parallel using 3 child processes
0:00:02 [1/1] test_idle passed
can't invoke "event" command:  application has been destroyed
    while executing
"event generate $w <<ThemeChanged>>"
    (procedure "ttk::ThemeChanged" line 6)
    invoked from within
"ttk::ThemeChanged"
1 test OK.
Total duration: 0:00:03