It would help to know what version/build of Moneydance you are running, see under HELP -ABOUT MONEYDANCE. e.g. 2017.8(1687).
Also what operating system you computer is running and if Mac what type of mouse?
The latest preview build includes a fix described in the change log as
"- improvements and fixes to mouse click handling, including working around over-sensitivity with Apple Magic Mouse-"