Somewhere along the way swtor changed the way it handled Printscreen. It dumps swtor screenshots into documents -> swtor -> screenshots instead of throwing them into the windows clipboard (so i can throw them into photoshop to work on them).
However, I run dual monitors, and I use Printscreen to copy and paste from other windows while I craft or chat on swtor, or to update my guild's website, and it is not grabbing any non-swtor screen grabs. Those captured outside of swtor seem to not register at all.
Printscreen functionality has changed so that if I need to grab a screenshot outside of swtor I cannot do so while it is running (unless I use the windows snipper tool that leaves an ugly red border around everything i snip).
I have encountered this as well and found that if you place swtor in windowed mode the printscreen function will work correctly even if the game is running. So for instances where you are working on non-swtor screen captures, the game will not interfere with what you are doing.
In relation to use the snipping tool, it does have an option to do a full screen snip if you do not wish to have the game in windowed mode. To get rid of that red border you can open the snipping tool, go to options and uncheck the box marked "show selection ink after snips are captured".
I hope that helps.