Errors in CAPI display callbacks are problematic for the Debugger tool, because they can be invoked repeatedly. In order to handle this situation, the display of a CAPI pane where an error occurs in a display-callback (a "broken" pane) is normally disabled until the Debugger tool exists. Therefore while debugging such errors some panes will not be displayed correctly.
This issue can also occur with focus related callbacks, such as
If it is not easy to fix the problem, exiting the Debugger tool allows the error to happen again. To prevent this, in some cases there is a restart to disable the display of the broken pane permanently. Once this happens, the pane is not displayed correctly.
LispWorks IDE User Guide (Macintosh version) - 25 Nov 2011