QGIS » QGIS Application

When adding labels via show labels for this layer, and a label is selected from a joined table, the result is no features are displayed. However, if a label is chosen from the main table, everything works OK.

I have three tables in MS SQL Server
table 1 = geometry table
table 2 = main table
table 3 = additional info
Layer 1 = table 1 joined to table 2, table 1 joined to table 3 (all via the same key)
Layer 1 is not visible
Layer 2 = table 1 joined to table 2, table 1 joined to table 3, table 1 joined to Layer 1 (all via the say key)
Features to be displayed are: Layer 1.name_field = "XX"
This is the only way I could think to implement the code snippet SELECT * FROM tables, WHERE parent_key = (SELECT key WHERE name_field = "XX)

With no labels are shown, the expected number of features are displayed. in Layer 2
If a label from table 1 is displayed sourced from either Layer 1 or Layer 2, it is displayed correctly
However, if a label from table 2 (either layer), then no features are displayed.