It seems when you use the mass comment features, more specifically the one triggered by : / Commenting does not comment the last line. It seems you work based on a line feed, so when we select our lines it does not do the last one selected.
When you say "last line" are you referring to the last line in a file? If so, does it matter whether there is a blank line after it? If this is the case, then we have seen this before. Not sure what the resolution was, if any.
I have also seen some strange behavior when selecting the text from the bottom up instead of the top down. Are you going up instead of down?
JPizzi, it seems that that is it, the direction of selection. Why is it that I must select from top-down? It is much more normal for me to select bottom-up.