i too got that behavior from that url and build 8469.
first I couldn't drop the components. then if i chg to sdk 4.0.0 i can, then when i chg back to 8469 it flattened them visually out at 0,0 but in the mxml it kept the coords as i orig dropped them.
I just assumed it was to do with changing flex4 to spark.
Goes fine with build before that and as soon as flex4 goes to spark, it breaks
All spark components show up in 'custom components' block
tinylion dev uk
The last time I did a build of the sdk was on the code just before you had the mini-freeze and all was perfect, When I first set up the work space there was a netmon error, When I pointed to netmon.swc I got a spark.swc warning so I removed netmon.
As mentioned in another post the co-ordinates for a component are correctly stored just not used for the design mode canvas, I was going to d/l the nightly build but I see that it has caused others the same problem.
Anyway I suppose its a bit irrelevant, as this beta has now expired.