Direcitonal inputs are noticably delayed and/or inconsistent in PBR viewers compared to non-PBR viewers, said delays being most noticeable when operating vehicles. Delays in inputs can result in key-presses that are longer than intended, or in some cases may result in no input being registered at all (the latter most notable again while operating a vehicle).
To test for the bug, it is recommended that the tester be proficient with vehicle operation, namely on the grounds of consistency, and that the tests be carried out on a closed circuit (and optionally one with a timing system).
Recommended testing locations:
Free race-ready vehicles ideal for these tests are available at the landing points.
The bug has so far been tested and discovered in the official LL viewer, Firestorm viewer, and Alchemy viewer. It is yet to be known if it persists elsewhere, but is highly suspected of being the case.
(This issue currently threatens the existence of racing communities as it has become vastly more difficult to safely control their vehicles)