Empty plain text content control

[Blegos]

Hi,
i insert plain text content control with Test method in VBA which has empty
placeholder text.
VBA Code
------------------------------------------------------------------------------------
Sub Test()
Dim cc As ContentControl
Set cc = Selection.Range.ContentControls.Add(wdContentControlText)
cc.Tag = "ThisTag"
cc.Title = "ThisTitle"
cc.SetPlaceholderText , , ""
End Su
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Then i go to document and turn on Design Mode ( Developer Tab ). Content
control has no value and if i turn of Design Mode warning message appear:
Word cannot turn off design mode because placeholder text in a content
control contains invalid items. Placeholder text cannot contain items such as
floating objects, revision marks, or content controls. Remove these items
from the placeholder text and try again.

If i place one space character in content control then i can turn off design
mode.

I think that content control must allow empty text inside, and that warning
is wrong.