Selection-Screen F4-help for Predefined Date Type 'd'

Apparently if a (selection) screen element is defined using the predefined ABAP-Type 'd', the automatic date help is not displayed. Tbh, i came across this problem for the first time today, when defining a utility report (for PoC purposes).

PARAMETERS:
  p_date1 TYPE d, " Without default 'date' help
  p_date2 TYPE dats. " With default 'date' help

I checked on the internet found that this problem is there since ages. However i couldn't find any relevant SAP documentation.

I have the following questions:

• Why this restriction for 'd'?
• Is this defined somewhere in the ABAP documentation? If not, shouldn't it be?

BR,

Suhas