Thanks for the report and script. I can't reproduce this with 3.7.1rc1 tag and also tried this on v3.7.0 which works fine on Mac OS running 10.10.4 and tcl version 8.5 . I checked out the 3.7.1rc1 tag and did a clean rebuild with `git clean -xdf && ./configure --with-pydebug && make -s -j4` and tried below

Steps I followed : 

* I executed the script.
* clicked on "click me" button.
* A file open dialog opened and I closed this with esc.
* Again clicked "click me" button and selected a file to click enter the file open dialog disappeared 
* Closed the main box with "click me". No segfault.

Since the report says it's a regression between 3.7.0 and 3.7.1RC1 I am adding Ned as a friendly ping about this issue so that this can be tracked better between RC releases.