Hey, I'm new here so forgive me if this has been asked before... 

I'm paying with some whole grain bread - it's Peter's Reinhart's most basic Whole Grain bread with a Biga and a Soaker.
The flower contains about 11% protein.  I think it's about 75% fluids.

The bread rises and looks all nice, I shape it and let it rise. The first time - it rose and "blew up" - became a low (rather airy) beard. The second time, I let it rise in a basket, because I was afraid it wouldn't hold. After rising it felt as if it had so much air in it that it behaved a bit like soft airy jello. As I took it out and into the oven it just lost most of it's air and I got the same rather flat airy bread.

As far as I can understand there may be several reasons:
1) Over rising? It was a stable dough after I shaped it, but as it rose it was very soft. I let it rise in the oven with a hot cup of water inside. Could that be the problem?
2) Too low gluten? Should I knead it for a longer time?
3) Wrong shaping method?  I'm just going for an old fashion round loaf so...
4) Too much hydration? I am following the directions with a scale :) 

Would love to hear your input on this,
Thanks in advance, Dvir