Zak,
Yes, I agree Zak that it may make more sense to have a message come up which says basically the same thing, but says, "Blah, blah, blah...do you still want to continue. Clicking on OK or yes would open the blank chart or the one not in the in box, and clicking No or Xing out of it would do the same.
But, all the warning message is designed for is to let you know that the chart you just clicked on whether in the patient list or the schedule is going to open no matter what you do unless you crash the program with task manager or reboot. This would allow you to know the chart should not be used to chart on given the inherent redundant situation with the saved chart in your box.
While your way may be better, it would seem to me that it would only be a lot better if someone were new to AC. Because either you would know you had a chart in your inbox to finish in which case you would open it there or you wanted to just open the chart to view it, and you don't care that there is one in your inbox, so you just click OK, and move on to your chart. Makes sense to me.