There is a measured 20+ db decrease in signal on the iphone4 when the antennae is bridged. If you are relying on the bar display alone to tell you if you have the problem, you are not getting the whole story. If you have a strong signal already, the signal attenuation will still put you in the 5 bar range. This does not mean that you dont have the problem.
See this chart for details:
See this chart for details:
