The sampling rate error problem is well-known, and is documented on the Tigertronics web site. I'd give you the link, but the Tigertronics web site doesn't display internal links in the browser, so I'll just reproduce it below:
11025 Hz Sample Rate offset error - Due to a Windows system issue, some Windows ME, 2000 and XP computers may show an abnormal sample rate offset error of around 7000 ppm at the 11025 Hz sample rate (other sample rates are NOT affected). If this offset error occurs on your computer, it can result in your transmit (modulation) frequency being off from your receive frequency. When operating digital modes, this can manifest itself in several different ways. With PSK31, other stations may not respond when you answer their CQ, or they may respond but say that you are off frequency. It can also result in both you and the person that you're talking to "walking" across the waterfall as each of you corrects your tuning after each transmission. On MT63, this problem can result in other stations not being able to copy you, or they receive your text in lower or upper case only, or certain characters such as spaces are missing.
This issue can be easily resolved in virtually all cases by simply changing the sample rate in your communication program from 11025 Hz to 12000 Hz. It's important to note that changing the sample rate will NOT hurt anything if this problem doesn't exist on your computer, so if you're not sure, we suggest changing it just to avoid the issue. Also, other standard sample rates (8000, 22050, 44.1, etc.) work just fine and do not need to be changed. It should also be noted that Windows 98SE and Windows Vista systems never show this offset error.
I've experienced this problem, and can attest to the fact that the fix described above works. Since this seems to be a Windows problem, I assume the fix would also work for other hardware interfaces.