Motorola XTS5000 + Earpiece

[HailStorm]

Hello.
I have a work-issued XTS5000 and a non-work-issued Earhugger receive-only earpiece. The 3.5mm connector on the earpiece stopped working recently and, with the help of a friend, re-soldered the end with a new connector. When plugged into things like my iPhone, it works fine. When plugged into the radio speaker mic (well, the part at the radio, not the mic itself), I hear audio transmissions in the earpiece, but also coming through the speaker mic.
We wired the ground to the ground, and the signal wire to the tip and ring (didn't have any mono connectors).
What's causing it to not cancel the audio to the speaker mic?
Thanks!
-Ted