Drumset menu

Hi,
I have the latest version of Musescore - just down loaded.
When I select the drumset under Instruments, I will usually start the measure with a bass drum from the drumset menu. What suddenly happens now is that I click on the bass drum in the drumset menu and immediately the bass drum note appears in the score. Before this never used to happen in this way. One would select bass drum and with the cursor place it in the score with a click. Now if I want to add, say, a closed hi-hat - it could be any of the instruments available in the drumset menu - together with the bass drum at the same point in the measure, this is now not possible. What happens now is if I select the hi hat from the drumset menu with the intention of placing it at the same point in the measure as the bass drum, immediately the hi hat will kick out the bass drum and the hi hat will be there in it's place. So I now cannot have the two instruments at the same time as was the case before.
Is there some new setting I have missed?

Thanks,

Henry