Determine if a folder synchronization filter is turned on
This is how to check and turn it on, presumeably the reverse would do it.
In the Navigation Pane, click a folder.
If a filter is turned on, Synchronization Filter Applied will appear in the status bar. Multiple Filters Applied indicates that both a synchronization filter and a view filter have been applied. You can quickly review the filter by clicking the arrow next to the text in the status bar, and then clicking Synchronization Filter Settings.
Review a folder synchronization filter
In the Navigation Pane, right-click the folder that you want to review, and then click Properties.
Click the Synchronization tab, and then under Filtered Syncronisation Click Filter