There is little more that I can add to the title statement.
1. Start IDLE
2. Go to *Edit* menu option
3. Select *Find in files...* option
4. Put some word in the *Find* input box
5. Press *Search files* button
When the command is issued the disappearance of IDLE's window is so quick that almost nothing can be seen. There is however a hint that a new window pops up with some message, that I have been unable to read. With some input strings or if the search is happening in a directory with many *.py files a quickly moving list of messages shows in this window, but the final result is the same: IDLE disappears immediately.