I experienced two weird issue, in general everything works perfect with the two signer accounts, I can deploy contracts even with browser-solidity, call them, transfer ether, etc.
However, if I use the user account (0x004ec07d2329997267Ec62b4166639513386F32E):
when I deploy a contract (using browser-solidity) with a library, the signer accounts (eg. 0x00Bd138aBD70e2F00903268F3Db08f2D25677C9e) has to accept two trx, and it's working. If a change the account to the "user" account 0x004ec07d2329997267Ec62b4166639513386F32E, only one trx has to be accepted, but browser-solidity does not return, the contracts are never deployed.
After some time, even transfer of Ether from user account does not work any more. I can accept the trx, but then it goes to pending trxs, which get never "mined". I can see a lot of pending transactions in etherchain-light, which obviously never get confirmed. Something is strange here, it worked at the beginning and stopped suddenly, queueing all trx from the user account in pending transactions.
So, in short: there seems to be a difference between signer accounts and user accounts which I do not grasp. But I would like user accounts to have the same privileges as the signer account.