FM tables: Ruling has a mind of its own

Using FM 8 on WinXP.

I've been using Framemaker since version 3, so I'm pretty familiar with the software. Here's my current situation:

I have a customized table format. The ruling is set as follows:

COLUMN RULING
1st: Very Thin | Others: Very Thin
Every 2nd: Very Thin | Others: Very Thin

HEADING AND FOOTING RULING
Separators: Very Thin | Rows: Very Thin

OUTSIDE RULING:
Top: Very Thin | Bottom: Very Thin
Left: None | Right: None

OK, everything is set to VERY THIN except for "outside: left/right" which are set to NONE. However, when I create a table, I always end up with every third row having its bottom ruling slightly thicker than the rest. You can barely notice in FM unless you zoom in to 400%, but it really shows up on the PDFs.

I've tries various combinations to try to unstick this, but with no luck. There is no custom ruling applied.

What's going on?

How can I get VERY THIN to mean VERY THIN EVERYWHERE?