Try going to View -> Filter -> Details (placing a checkmark by it by clicking it)
This should filter all Detail brushes and allow you to see if you accidentally made outside structural brushes into a detail. This would of course, leak the map.
Otherwise, you could try hiding all the entities and copying the geometry to a new map to see if that helps narrow it down to an entity problem.
When you say 1.4 I assume you mean y ou are using 1.5, and I dunno if there are any bugs in it as I haven't messed with 1.5 at all. It's possible there was a bug in it that borked your map file or something, but there are some more things to try before we get that far.