[quinta@ebf.cz]

Hm. Seems the issue is somehow influented by compatibility mode of source docx.

In vanilla docx, inline image is converted as expected.
When source docx is set to compatibility mode (docx saved as doc, then saved as docx again, with "compatibility mode" option; Word 2013, 32b, czech localization), inline image is converted as "display: block". Sample docx and epub files attached.

On the other hand, original sample docx is in compatibility mode, too. And conversion issue is not detected...