Audio Needs Rendering After Modification

Question

I have a 48.00 KHz, 32-bit Floating Point sequence.  My primary audio is 48.00 KHz, 16-bit, so no rendering needed.
I am also using some sound FX at 44.1 KHz, so they need to be rendered.  I recently learned about SEQUENCE > RENDER ONLY > ITEM LEVEL.  It works fine, and even if I make changes to the 44.1 track thereafter, there is no need to render again.
Here is my problem: Most of my project was rendered using SEQUENCE > RENDER ALL > BOTH.  I have up to 8 audio tracks and now, when I add audio, even 48.00 KHz, I have to rerender everytime I make a change, e.g., volume or position on the timeline.  I try RENDER > ITEM LEVEL, but it doesn't do anything.  The only render option that works is RENDER ALL and I have to do it after every little change.
Thank you!

Answer 1

I'm just very confused.  Now, when I put two identically created 48.00 KHz audio tracks in the timeline, I need to render; however, by themselves, I don't need to render. 
Also, when they are together elsewhere on the timeline without any other audio tracks, I do not need to render.  For some reason, in one particular spot, I need to render if they are together.  If I inch either one along the timeline, the render bar goes away.
I've tried closing and reopening FCP.
This is really wierd...