Bunion hurts when it has been taped and straightened, why is this?

Something is : Obviously aggravating it, you don't mention if the pain is at the site of bunion or joint? Taping is not an effective means of straightening out a bunion anyway. Most taping lasts a very short time according to medical literature, so not sure it's worth the bother.

Joint Adaptation: As the bunion deformity progresses, the articular surface of the metatarsal head shifts laterally(leans toward the second toe). This adaptation develops over the years. The joint gets used to this position. Attempting to staighten the toe changes how the toe articulates with the metatarsal bone. This can lead to irritation of the joint. In surgery, we tilt the bone to address this deviation Dr L

Consider seeing a MD: If your bunion remains painful despite sensible shoe wear (wide, flat) and taping or bunion pads then this is generally a good time to consider surgery which with modern techniques is very straightforward. Taping the toe into the correct position may hurt due to- - stretching out and irritating the tight tissues on the lateral side of the joint - there may be early arthritis in the joint

Could be : 1) tape is too tight 2) sometimes bursitis/ inflammation develops oer the bunion and the tape is pressing against it 3) the tape takes up room in a shoe making the shoe tighter 4) may have arthritis in the joint so the way you are positioning the toe is causing bone on one movement. 5) the joint could be track bound meaning it doesn't want to be straight and by you forcing it....Pain results.