Double-clicking is making a ^C

Sometimes mouse double-clicking causes a program to terminate.

This is occurring because the double-clicking selects a word and the word is copied to the clipboard. At this time, a Ctrl+C event occurs. This is not an Xshell feature nor a bug.

Certain third party programs act on selected text and creates a keyboard event of Ctrl+C to copy the text to the clipboard.

We do not recommend you utilize such a feature when using Xshell. Try disabling the program or creating an exception for Xshell in the program.