Should substitute-command-keys remove text properties of strings containing quotes?

[Clément Pit--Claudel]

In Emacs 25, substitute-command-keys removes text properties of strings 
containing quotes. Is this expected?

> In Emacs 25:
(substitute-command-keys (propertize "`a'" 'prop 'val))
"‘a’"

> In Emacs 24.5:
(substitute-command-keys (propertize "`a'" 'prop 'val))
#("`a'" 0 3 (prop val))

For more context, here is how I came across this issue (slightly edited example 
from a package with defcustoms with large `set's of options):

(defcustom my/pretty/set/option nil
  "Demo text properties in customize."
  :group 'emacs
  :type `(set (const :tag ,(concat (propertize "Title of option 1 (bold on both 
24.5 and 25)" 'face '(:weight bold))
                                   "\n   "
                                   (propertize "Docs of option 1, in a smaller 
font on both 24.5 and 25." 'face '(:height 0.9))))
              (const :tag ,(concat (propertize "Title of option 2 (`bold' on 
24.5 but not 25)" 'face '(:weight bold))
                                   "\n   "
                                   (propertize "Docs of option 2, in a smaller 
font on 24.5, but not 25." 'face '(:height 0.9))))))

This example uses text properties on `:tag's to make the customize buffer more 
readable. This works fine in GNU Emacs 24.5, but it stopped working on master 
(and emacs-25), because of substitute-command-keys replacing quotes and as a 
side effect dropping text properties.

Is this change expected (making the example above a misuse of text properties), 
or is it accidental? If it is not expected, I can open a bug report.

Thanks,
Clément.