Depending on the type of pipe and age, there could be some blockage. Not sure how the bubbles are getting past the kitchen p-trap? Those bubbles should work up to the vent pipe, not your sink.
If you really want to check, remove the p trap and have apan or water bucket handy. Place a few inches of clear water in the tub and let it drain. no water should come out of the wall pipe under the sink. Then try it with the bubbles. I'll suspect that clear water will back up slightly and into your bucket. That should not happen.