External USB hard drive doesn't mount until reboot

Hey there. I bought an external USB hard drive (a 250 GB drive by ComStar) last week, and I'm having trouble getting it to mount. The first time I plug it in, it works fine and shows up on the desktop. When I remove it (having properly ejected it first) and plug it in again later, it doesn't show up. It's not on the desktop, it's not in Disk Utility, and it's not in /Volumes (via the Terminal). If I reboot my Mac, it's there again.
Has anyone else had this problem with external drives? Are there any solutions or workarounds?

The first time I plug it in after a boot up. It doesn't matter if my Mac has been up for three weeks -- if it's the first time I've plugged in the hard drive since the last reboot, it always works perfectly.
It's very strange and annoying. It's almost like it's not getting ejected properly.
That being said, I just ejected and unplugged it, waited five minutes, and plugged it back in. The stupid thing worked this time. It's driving me nuts! I don't mind things that don't work, but things that work sometimes are really frustrating. If no one else is having this issue, it's probably something unique to this particular drive.

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