This has been an issue for a while now, but it's really starting to irritate me. I tend to type a fairly large amount of notes for my workouts. With the new multisport layout, this becomes even harder. I'm a triathlete, and often try to describe the Swim, T1, Bike, T2, Run, and Race Recap all in 1 document. Even if I only write a couple of sentences about each section, it still won't fit. To make matters worse, Google Chrome spell check doesn't work in the Notes text box. Also, if you write your notes and then try to name your activity and select the activity type, all your changes will be lost, not just your notes.
TL;DR Allow for a bigger character limit on Notes text field and enable browser spell check in the text box.