Other mistake: After getting on aboard the dirigible, Henry is holding a German newspaper when addressing Indy. But he'd have a hard time reading it as it's upside down. Even if he's just trying to hide, holding an upside-down newspaper would draw the attention of suspicious guards.
Suggested correction: Henry Jones Sr. doesn't have his glasses in this scene. He can't really see anything on the newspaper, that's why he is holding it upside down.
I'd say that, more than anything, a hasty attempt to blend in would be more likely the culprit. Even without the spectacles, Henry, being the fastidious person he is, would have righted the paper, with or without eyewear.
But since he couldn't see the letters, how would he have righted the newspaper (or even noticed it was upside down)?
Ipon! (Japanese for "point.") I can see your point; however, I would ask that the following be considered: that there is usually more than just letters and words in newsprint. Even if not viewed, pictures are good indicators of the newspaper's orientation.