On MW 1.24 Vector skin, with the user preference ticked or unticked, the sidebar still has items collapsible. The $wgVectorFeatures set to true or false only makes the option come and go from preferences, not enable or disable the collapsible items in the sidebar.
It's the same with 0.1.3. Ticked or unticked, the sidebar still has items collapsible.
Also with CollapsibleVector commented out in LocalSettings.php UserMerge 1.9.0 still gives "Fatal error: Function name must be a string in ..../w/extensions/UserMerge/MergeUser.php". It's deleting the user page (on this wiki it gets created by the user registering) that allows merge and delete to function.
Try earing your cache I have enabled it to do it global and in your preference it should show that it is ticked if not tick it and untick it and then clear cache see if that works. If not I will have to see why it doesn't work. Because the patch works for me.