Quick search

What is your primary language set on the vault ? Looks like it's english so it takes "Mark" and "Bygg" (the letters left after Mark) separately..

Or if it's Dutch (I assume that is Dutch :D ) you can try to reindex. 

userguide.m-files.com/.../backing_up_and_restoring_the_vault_search_index.html

The primary language is set to English and the secondary to Swedish.
So you mean because that "markbygg" isn't a english word then it tries to split up the word and that is why it works with "" because then you force it to search on the entire word?
We are operating in Sweden, Norway, Finland, Germany and the Baltics. The majority of the documents are in Swedish, would it be best to change the vault language to Swedish instead?

I have also heard that there is something called Smart Search one could use instead of dtSearch, would that be any good for us in this case?

The primary language is set to English and the secondary to Swedish.
So you mean because that "markbygg" isn't a english word then it tries to split up the word and that is why it works with "" because then you force it to search on the entire word?
We are operating in Sweden, Norway, Finland, Germany and the Baltics. The majority of the documents are in Swedish, would it be best to change the vault language to Swedish instead?

I have also heard that there is something called Smart Search one could use instead of dtSearch, would that be any good for us in this case?

I'd either go and test this (setting Swedish as first language) on a test environment or ask it directly to support. IMHO Switching to Smart Search wouldnt do any difference in this case

Ok thanx! Will a change on the language be a big thing almost like a reindexing or a task that would be pretty quick and easy for the system?

It should be doing whole indexes all over again. Depending on your vault size, it would take days. 

I'd definately do it on a test vault first.