I say deliberate because there is a commit introducing exactly this
behaviour:

56cd178caebd061c992d4c7c682d0e4dc2c40f26
Author:     Nicolas Goaziou <mail@nicolasgoaziou.fr>
AuthorDate: Fri Aug 21 14:44:26 2015 +0200
Commit:     Nicolas Goaziou <mail@nicolasgoaziou.fr>
CommitDate: Fri Aug 21 14:44:26 2015 +0200

org-indent: Fix indentation in inline tasks

* lisp/org-indent.el (org-indent-add-properties): Indent inline tasks'
  contents according to current outline level, not inlinetask's.  This
  is consistent with hard indentation, using `org-indent-line'.

If others think that this default should be changed, they are free to
jump into the discussion.

Best,
Ihor