Power Query Merging on GUID Columns

Scenario: You are merging two tables in Power Query on GUID columns with Text data type. In my case, the first table (UserDim) came from Azure SQL DB and the second (systemusers) from Dynamics CRM, but I believe the source is irrelevant. Then, you expand the second table in the next step after the merge, select the columns you need, and see expected results in the preview pane. However, when you apply the changes, the related columns are not populated (empty) in the Power BI data model. In other words, the join fails to find matches.

Solution: I think there is some sort of a bug in Power Query. True, Power Query is case-sensitive so joining on the same text that differs in casing in the two columns would fail the match. However, in this case the guids were all lower case (or at least that’s how they appear in the preview). The only way I could explain the issue is that the refresh somehow converts the guid values to different casing before the join is performed. Anyhow, the problem was solved by adding an explicit step to convert both guid columns to lower case before the merge step.