aggregate_mapping() type checker performance issue

Pike v8.1 release 18 running Hilfe v3.5 (Incremental Pike Frontend)
> int t = gethrtime(); typeof(([ 1: `==, 2:`<=, 4: `< ])); gethrtime() - t;
(1) Result: mapping(int(1..2) | int(4):function(int | float ... : int(1bit)) | function(string ... : int(1bit)) | function(program | type(mixed), program | type(mixed), program | type(mixed) ... : int(1bit)) | scope(0,function(int | float, int | float, int | float ... : int(1bit)) | function(($0=array | mapping | multiset | string), $0, $0 ... : int(1bit)) | function(function | object | program, mixed, mixed ... : int(1bit)) | function(mixed, function | object | program, mixed ... : int(1bit)) | function(type(mixed), type(mixed), function | program | type(mixed) ... : int(1bit)) | function(($0=array | mapping | multiset | string), ~$0 ... : zero)) | ~function(~mixed ... : mixed) & function(mixed ... : int(1bit)))
(2) Result: 40760
> int t = gethrtime(); typeof(([ 1:`==, 2: `<=, 4: `<, 5: `> ])); gethrtime() - t;
(3) Result: mapping(int(1..2) | int(4..5):function(int | float ... : int(1bit)) | function(string ... : int(1bit)) | function(program | type(mixed), program | type(mixed), program | type(mixed) ... : int(1bit)) | scope(0,function(int | float, int | float, int | float ... : int(1bit)) | function(($0=array | mapping | multiset | string), $0, $0 ... : int(1bit)) | function(function | object | program, mixed, mixed ... : int(1bit)) | function(mixed, function | object | program, mixed ... : int(1bit)) | function(type(mixed), type(mixed), function | program | type(mixed) ... : int(1bit)) | function(($0=array | mapping | multiset | string), ~$0 ... : zero)) | ~function(~mixed ... : mixed) & function(mixed ... : int(1bit)))
(4) Result: 42070381

The time taken for the second statement is ~42 seconds (~1000 times slower than the first). Doing

> int t = gethrtime(); typeof(([ 1:`==, 2: `<=, 3: `!=, 4: `<, 5: `> ])); gethrtime() - t;

essentially hangs the compiler.