This concerns me, and it's happened more than once...

When trying to send a Canvas email to a student, I write out the message but then realize that I need to add links or other information into the body of the message. I try to select all the text, then copy it to the clipboard so I can ensure that if I have to restart the message, at least I have the text copied. However, during the text selection, where all the text becomes highlighted, my pending email just disappears. No text copied. 

It acts like my cursor somehow sweeps beyond the 'border' of the email text entry field which somehow cancels the whole process.

Can I get some insight into what may be going on? Again, this has happened several times, forcing me to rewrite, from memory, an entire message.