Title pretty much says it all.

So I was about to write a "something else must be going on here" reply, but figured I'd better check before spouting off too much.

Tested 9.2.1.71 (IntelliJ dev environment, one other mod, forges 39.0,9 and 39.0.19 both), and... normal behaviours of LMB and RMB are indeed reversed. It's surprisingly disconcerting.

Edit: R and U are also reversed. JEI "show recipes" and "show uses" key binds are correct.

Edit: R and U are also reversed. JEI "show recipes" and "show uses" key binds are correct.

Yup. Checked all that as well.

Thanks for the report!
This has been fixed in the next release, which should be available shortly.