In Algiers, I followed Omar's servant but every time he disappears into a house, I can't seem to find Omar's house. There is no indication of where Omar's house is. The location should be selectable on the map it didn't seem to work for me. I followed his servant many times and still can't enter Omar's house. Is this a bug?

You have to follow him very close. As a help, you can give him a red fez so it's easier to follow him.

You have to be close to him when he moves into the house. One thing that worked for me (when I didn't give the servant a fez, because I wanted the IQ points), is to first try to follow him, and watch where he moved into the house. Then I went back to the market and convinced the servant to go again, and then I waited at the spot where he disappeared last time, so Indy could see where he went. Not sure whether that works every time, but worked for me...