+RTS -S inserts only the last three commas into large allocation sums

A large Agda run with +RTS -S produced:

1975360908    148056 1010000424  0.02  0.01 14037.87 14215.63    0   46  (Gen:  0)
     4096                      0.00  0.00

4153,641,888,148 bytes allocated in the heap
   8,304,985,852 bytes copied during GC
     730,638,996 bytes maximum residency (15 sample(s))
       2,092,752 bytes maximum slop
            3236 MB total memory in use (25 MB lost due to fragmentation)

  Generation 0:  1791 collections,     0 parallel, 115.72s, 117.66s elapsed
  Generation 1:    15 collections,     0 parallel, 34.51s, 68.83s elapsed

  INIT  time    0.00s  (  0.00s elapsed)
  MUT   time  13887.63s  (14029.14s elapsed)
  GC    time  150.24s  (186.49s elapsed)
  EXIT  time    0.00s  (  0.02s elapsed)
  Total time  14037.88s  (14215.64s elapsed)

  %GC time       1.1%  (1.3% elapsed)

  Alloc rate    299,089,110 bytes per MUT second

  Productivity  98.9% of total user, 97.7% of total elapsed

The bytes allocated in the heap number has only three commas inserted, while I'd expect four...

Trac metadata

Trac field	Value
Version	6.12.1 RC1
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Runtime System
Test case
Differential revisions
BlockedBy
Related
Blocking
CC
Operating system
Architecture