Yep, happening for me in the ABD Forum, too. Sigh. Both Chrome and Firefox.
What I've noticed by looking at multiple threads is that it's post #6 and #8 that are being put up in the right-hand corner of the page, instead of in-line like all the other posts, so it smashes posts #1 - #5 & #7 over into the left-hand side of the page. Everything after post #8 (#9 - #20) is formatted normally.
Can I mention that another thing I noticed (don't know if it's really relevant or not) is this appears to have started happening when the bright orangey-yellow adds started showing up at the top of the page.
Sayhello