I had an issue a little while ago my object selection was being canceled by autocad when I initiated a command. I thought maybe my pickfirst had been reset to 0 (causes autocad to ask you to select your objects after your command when 0) because of a crash. I discovered it was set to 1 so that was not the problem.
Then after a little sleuthing, I discovered that the command lines for some of the macro command lines in the Customizable User Interface were prefaced by ^C^C_. This is done in order to cancel out any previously initiated commands that might interfere. However, this also clears your current object selection as well.
To stop this, you need to go into your CUI (type:CUI) and scroll down to the command causing you issues. See the attached image for an example of said prefix in the macro for the properties command. All you need to do is delete it, apply the CUI settings, and hit OK.
You are now good to go.
