Also make sure your availability filter is set to something that makes sense in your case. The 1.8 sneaky peek has moved the due and flagged related options from the availability filter to the status filter, so you may end up with different combinations of settings than you're used to in previous versions.
For instance, in OF 1.7, the "Due or Flagged" option was on the Availability filter, and this overrode the "available" behaviour to show all tasks that met that criteria, regardless of whether they were available or not. In the 1.8 sneaky peek, you can now have the availability filter set to "available" and the status filter set to "due or flagged" which will show only those tasks that are "due or flagged" AND available.
So if your project or action group is set to sequential order, later tasks may be blocked in this case regardless of whether they have an inherited due date or not, since you could have the filter set to show only available tasks. You'd have to set the availability filter back to "Remaining" to get the old 1.7 behaviour of showing all remaining due or flagged tasks.
If you're using perspectives inherited from 1.7 or prior, you may need to adjust them to account for this, since I'm not sure exactly how they migrate (I was so excited about having the separate "Due or Flagged" option in the Status filter that I didn't bother to check, I just jumped in and updated my perspectives right away).