IR/UV cut filter question

I have a modified Nikon D50, in which the original filter was replaced with clear glass. I bought a 2" Baader IR/UV cut filter to use with the camera for imaging. My understanding is that if I were to use this camera on a purely reflective system (like a Newt with no coma corrector) I would not need the filter, since the IR and UV that now reaches the sensor would focus with the other wavelengths. On a refractive system where CA would be an issue the filter would be needed. I assumed that when shooting through my C11 with a focal reducer and corrector the filter should be used. On my recent dark sky trip, however, I forgot to install the filter and proceeded to shoot an hour's worth of M51. The resulting image looks every bit as good as any of my previous images taken with the filter. No halos around stars or other visible effects. Granted, there are no really bright stars in the field. So the question: Should you use the IR/UV cut filter on an SCT w/FR, or not? I realize that the answer may be that none of my images are of sufficient quality for the difference to be apparent anyway! Any input from the experts here would be appreciated!

When you deep stretch the image, that's when you begin to see the effects on stars. Here's an example where a UV/IR filter would have helped: http://www.danilopivato.com/tabulae_coeli/1300_n30/m3_brc_hires.htm

And here's what it should look like (courtesy of Anthony): http://www.perseus.gr/Astro-DSO-NGC-6205.htm

Rolando