The sites I have updated to 7.3.4 still have problems with editing in IE 11. This forum site does work, however. Not sure what software it is using.

I found a couple of work-arounds in IE 11 that might help some people until this gets solved:

When pasting from Word, use the drop-down:  Paste Plain Text. The paragraphs come in with br tags between them, but at least it is something.

When trying to edit the properties of an image and the OK button does not work, just give up. Delete the image and while inserting it again, change the Properties tab to have the values you want, then click the Insert button. That works.

I really hope this gets fixed in 7.4.0.