This has been breaking all over in my codes too (as seen above), ditto on the preview pane working and the entry itself being a big guessing game.

A quick fix that worked for me (at least last night) was to add styling to it to force it to work, (minus the spaces):

< img src="URL" style="width:250px;" >

It's not normally what I do when quick coding simple entries either, but it did get the page to respect the code.