I will try to explain the cause of the problem. For example, if you enter the following text in MultiLine
textbox :test after test
In the database, the data is saved as three rows:test after test
So when you switch to Advanced
textbox will display just the first row and that causes the problem i.e. test after test
As a workaround, I would suggest you enter the text without breaks in order to be saved as one row.
Hope this helps.
the Telerik team