Click send twice in Apple Mail

Hi Everyone
Anyone got a fix for this? Apple Mail has suddenly started requiring two clicks on the send button (paper aeroplane) for the message to be on its way. Thus my automation with Keyboard Maestro has stopped working because it is set to simulate CMD + Shift + D once, (Which has been working for six months now) and manually, I write an email, click the send button and nothing happens. Click it again and away it goes.
Yes I have done the reboot and whilst the very first email I send works with one click of the send button, every subsequent email requires two.
I cannot find any forum on the net with this problem.
Thoughts anyone?
Cheers, Russell