I am using 18.3 64Bit Cinnamon.
I noticed that on the welcome screen (which is great BTW) activates the applications with only one click of the mouse. So, the application would open twice if you double-clicked the mouse. I also noticed that there is no cursor change while we wait for the activated icon/application to respond. So, if the PC is slow to open the ICON application then you could get three or even four windows opening...