Windows 7 - Explorer opens network drives twice

At the "computer" level in Windows Explorer, opening a drive results in one of three situations, unpredictably:

1) (rare, but what I want) -- the same window is used to display the contents of the drive.

2) (opening local partitions/disks usually gives this result) a new window opens with the contents of the drive.

3) (opening network shares usually gives this result) TWO new windows open, duplicates, showing the contents of the drive.

The double-window situation seems to most commonly occur when either on a network drive or on a local drive which may not be ready (i.e. not spun up), though I can't characterize why/when it also does this for the built-in SD card reader... sometimes.

I've made sure it's not fat-fingering the mouse button by reproducing the results with the enter key. "Open each folder in the same window" is checked. Any suggestions?