The effect of
current-process-unblock-interrupts stays in force until the next call to either
current-process-block-interrupts, or an exit out of the scope of a surrounding allowing-block-interrupts or with-interrupts-blocked. Inside this range bodies of allowing-block-interrupts and with-interrupts-blocked have their own state, but they restore it on exit.
LispWorks User Guide and Reference Manual - 13 Feb 2015