Problem startingup in Mac OS from Boot Camp

Over the last few months, switching from Boot Camp Windows back to Mac OS has become increasingly fraught. At first, clicking on the diamond symbol in the Windows tool line was enough. Then, when that stopped working, I would switch to the Boot Camp application within windows in order to start up in Mac OS.

After that seemed to also pack up, I discovered that pressing the alt key while restarting would work instead, taking me to a screen which offered a choice between Mac and Windows. Now, even that alternative has started failing increasingly often; the last time I came out of Windows, I had to repeat the process six times. Now I'm reluctant to even try Boot Camp, for fear I'll be stuck in Windows permanently. Can you please help?