Similar thing when calculating the road to the Pula from Makarska. From Slavici to Gorenja Vas the highway is ignored. Looks like a bug or something. Also I don't know why it doesn't calculate smart roads, It always sticks to the fastest or the shortest and roughly accepts roads priories - this gives strange routes calculations.
The problem with Makarska-Dubrovnik is caused by changing borders. Border for Bosnia was generated from http://www.openstreetmap.org/browse/relation/214908, which is no longer available. Backup was used but it is slightly shifted so the border points do not match [that's my current theory]. Croatia conversion failed (problem with water area) so the data are also from different "batches" ... I will investigate it more. thanks Martin
On Early Maps Access is now available bosnia_and_herzegovina_osm_130729.mca with new border relation. Now the countries "fit" and routing is on D8 as you would expect. thank you Martin