Yet again, please try not to see too much into it. Jolla is not a friendly club, it is a corporation. They are not being "open and very professional", they divulge as little as they possibly can.

When will the next update come out? They made a vague promise a long time ago that they will "endevour to publish one monthly". Does that bind them in any way? Of course not. Therefore they are free to do as a normal corporation does and keep it to themselves until the release time.

The tablet is a different animal. They made a very specific and public commitment to deliver by the end of May. Does that bind them? Of course it does! Now they've realized they cannot deliver on the given date. What options do they have? They have to make another announcement with a revised release date. Not just a vague one ("tablet will be delayed"), but a specific one, such as "end of July".

It has nothing to do with openness. Jolla is not special. It is what any corporation would have to do.