There's a related anomaly that has been around a long time.

% interp create slave
slave
% interp alias {} b {} break
b
% while 1 b
% interp alias {} b slave break
b
% while 1 b
invoked "break" outside of a loop
% catch {slave eval break}
3
% catch b
1

This is related to some of the "knownBug" tests in interp.test