Congrats!
But I don't know really if it is a bad thing to use the grounding of the bike to make a total circuit. Honda used to love to do it with indicators (and so did MZ when they used the bar end type). Though I could see why it might interfere when you have 1 on the front and 1 at the rear, maybe.
Oh well. At least you got it fixed! There have actually been a few threads on this very issue over the years with the US TS250's, without a concrete resolution I don't think... So this might be nice to link to for those people of the future who also have the same issue.