While wearing the soujourener's sash, you can not pass over a slab if another slab is 2 blocks above it. This is possible in vanilla.

To confirm, it isn't the trodden dirt's fault.

You can hold shift, should be able to do it.

It's a vanilla thing, more info in #1014

No, I can walk into it without a sash in vanilla. With the sash, I just had to hold shift.

It doesn't work if you don't wear the Soujourner's Sash, either. This isn't a bug in Botania, it's in Vanilla.

That's the same bug that prevents you from walking up from soul sand into a 2 high area. Since you can step up higher it's just somewhat magnified.