Hello, Robert
When they mention the UCSC browser, is your user using the 'Get Data -> UCSC Main table browser' tool or are they trying the 'display at UCSC main' link within a dataset in the history panel (which leads to the UCSC genome browser display application)?
Does this problem still happen or happen in a reproducible way? If you've seen it happen, could you use firebug (if you use firefox) or the chrome developer tools (if using chrome) to see if there are any browser/client-side errors?
If you have access to the channing server logs (for galaxy), can you see any errors around the time this happens?
Thanks for letting us know and for the extra information,
Carl