Chuck --

Be aware that although the 3-tab sockets (and plugs on the bulbs) are physically the same, the wiring to them is different. You must rewire the three wires going to your original sockets in order for them to work with the older style bulbs. (BTDT)

You're seeing the effect of "crosstalk" between the two filiments in each bulb. When you get the wires hooked up properly, all will work fine.

Don't cut and splice. Instead, remove the connectors from the plastic sockets and re-insert each one in the correct hole for the older bulb.

I've done, it, it works great.
--
Don Foster (near Cape Cod, MA)