64-bit Preference Pane Displays Window

I've developed a preference pane which initially was being built with the Architectures build setting set to "32-bit Universal" (was the default). This caused System Preferences to relaunch in 32-bit mode but the preference pane worked fine.

I switched Architectures to "Standard (32/64-bit Universal)" and set garbage collection to "Supported". System Preferences no longer reloads into 32-bit mode, but when it runs it first opens my nib's window outside of System Preferences and for a split second I see all my controls in that window. The controls then move to the System Preferences window, but the window sta开发者_如何学Pythonys behind with nothing in it.

How do I get rid of this window?

In Interface Builder, there is an option on the window to the effect of "Visible upon launch".

Is that enabled? If so, try disabling it.