02 Trailblazer, weird blinker issue

I bought this trailblazer last week, and since then I have replaced almost every bulb. While replacing the headlight bulbs today, I decided while I had everything apart to check the rest. I checked the front drive side blinker and it worked fine. I checked the front passenger side blinker and it worked fine, but while it is working, the front driver side faintly flashes also. Does the blinker bulb need replaced?

I went out switched the bulbs from side to side, and now they work fine. Anyone know what might have caused that?

You may have just cleaned the contacts on the bulb by removing and reinstalling them, watch for the same thing to happen again.