I noticed with slime 2009-08-11 and xemacs 21.5.29, pressing v in sldb to show the source no longer works. I narrowed down the issue to the call to display-buffer in slime-show-buffer-position. In xemacs, the fourth arg to display-buffer is supposed to be a buffer (or nil); it doesn't like T as an argument.

From the docstring this is intentional. My workaround was to change the 4th arg to

(if (featurep 'xemacs) nil t) I suppose that could be just (not (featurep 'xemacs)). Ray