Originally Posted by Unca_Sam

I'm not sure why you decided to mix spokes, but it doesn't make a difference if you aren't using a tension meter to gauge your repair. If you have a musical ear (notes sound different) you can get your spokes in sufficient tension by listening to the tone made when you pluck a spoke. The thinner gauge butted spokes you bought will not sound the same as the straight gauge spokes, less material means they'll likely have a higher pitch at proper tension.

How are you gauging true on your wheel? Are you using the fork and brake pads, or a stand?

Another thought, to address the cause instead of the symptoms: You broke three spokes on a front wheel, which to me indicates damage to the rim if the wheel otherwise gave great service. Spokes fail because of tension loading cycles, if a spoke is too loose, the repeated tensioning will cause it to fatigue and break. Rim damage, like a flat spot, will allow spokes to relax enough to eventually break. If you haven't already, check your radial true, or how round the wheel rim is (with the tire off).

Worst case scenario, if you can't figure it out, you can bring it to the bike shop for a repair and true!