I just tested the Custom Field ToolTip in my localhost. ToolTip is working just fine with CleanMart.
So it can't be any overriding issue or what so ever (I didn't think so, but i tested anyway -- because we have never used ToolTip anywhere on CleanMart; so we didn't touch it). I highly suppose it is a jQuery Conflict issue that prevents tooltip to work on your website.
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regards.