This known issue only occurs under the following circumstance: An URL containing ( and/or ) is copy-pasted or manually entered in the ow.ly Shrink URL box and then clicking "Shrink It". ow.ly will then strip the ( and/or ) and the resulting ow.ly short url will redirect to the wrong source page.
We are currently investigating the cause of the problem, and when we have discovered it, we will submit a fix.
In the meantime, if you need to shrink a URL containing ( and/or ), you've got to manually replace every occurance of ( with %28 and ) with %29.
We will update this article again once a fix is in place.