Why does this POSIXct or ITime loses its format/attribute

Question

here is my sample data, I do not understand why the ITime column loses it\'s format in the following code using the data.table package

Answer 1

Update: This has been fixed in v1.8.11. From NEWS:

:= (assignment by reference) loses POSIXct or ITime attribute while grouping is now fixed, #2531. Tests added. Thanks to stat quant for reporting here: Why does this POSIXct or ITime loses its format/attribute and to Paul Murray for reporting here on SO: Cannot assign columns as.Date by reference in data.table

Please write back if I seem to have overlooked something.

Answer 2

Filed as bug #2531, priority updated by Matthew.