If there are CAPI interfaces on the screen (other than the LispWorks IDE) when session saving is invoked, these interfaces are destroyed and then displayed again. Note that the display will occur in a different thread than the one running the interface before the saving (which was killed when the interface was destroyed).
If an interface (or any of its children) contains information that is normally destroyed (in some sense) in the destroy-callback, this information can be preserved. For the details see
capi:interface-preserve-state in the
CAPI User Guide and Reference Manual
LispWorks IDE User Guide (Unix version) - 13 Sep 2017