I pretty often hear native German speakers using the word order of a question in a declarative sentence.
E.g.
Habe ich doch gesagt!
or
Habe ich kein Problem damit.
Is this an acceptable form, or are those people just unaware of the grammar?
Update
The last sentence is an example I heard just today (not for the first time however). The whole (spoken) conversation did look like:
-- Wenn du nicht aufpasst, ist dein Glas schnell weg.
-- Habe ich kein Problem damit.