The reason is that due to Dwolla having a tendency to lock funds at will
This is not what has been happening and is not what happened here.
Can you name one instance where Dwolla has locked funds? [* If you are thinking of the "30-day probation" restriction as being a case of "locked funds", that's incorrect, and see below for that.]
There was one report of "locked funds" and it was that the user had to verify identity, but there have been no reports that Dwolla has ever locked customer funds once the customer has provided identity.
With Dwolla, all account-to-account (A2A) transfers are instant. This means that the second I transfer funds from my Dwolla account to yours, I no longer have access to those funds and you have the ability to spend the funds immediately. This is not hours, minutes, .. this is instant, like before the page showing the transaction status has completed.
In this specific instance, the problem is that Mt. Gox is not processing the withdrawal request in a timely manner. They have acknowledged this long-running problem (a problem that started in April), and have said the problem will be gone within a matter of days thanks to recent developments.
[* New Dwolla accounts are placed on a "30-day probation" where they have the restriction that funds cannot be sent to four specific Dwolla accounts -- those of Bitcoin exchanges. The probation period starts the first day that the funds have successfully been added to a Dwolla account from a linked bank account. Once the 30-day probationary period has passed, these accounts can send to Bitcoin exchanges just like any other Dwolla account. This is not "locked funds" though. During this probationary period the Dwolla customer can return those funds back to their own bank account, trade with other Dwolla users, spend the funds at other Dwolla merchants, etc., .... so the funds are not locked or "frozen", they just can't be send to these four Bitcoin exchanges right away.]
