Question about sends and phase

sharke
Let's say I have a dry bass signal on a track, and I want to send a little of it to a bus that has a bass amp on to mix a little grunge into it. Is it customary to flip the phase on the send track? I'm a little in the dark regarding issues of phase. 
 
The reason I ask is because if I do the above with Mark Studio on the amp bus, I get a drastically different sound if I flip the phase switch on the amp. Also, if I use the same technique but with the Aphex aural exciter, sometimes the results sound a little phasey. 
 
One weird thing I've noticed doing this technique, is that if I loop a section of the track in question when I first fire up the project, and play back that loop, the first iteration of the loop will sound normal. But when it returns to the start for the second iteration, the phased effect begins, and remains for the duration of that session (i.e. until I close the project and reload it). Not sure how significant this is or if it's just another one of those oddities that happens when looping in Sonar. 

bitflipper
To get back to the original question...you might need to flip the polarity when combining direct and miked versions of the same signal. It depends on whether the speaker is in phase with the amplifier's line output or DI box, which it usually is, but isn't guaranteed. 
 
What's more likely is that you have to adjust the phase relationship between the two signals because the amplified signal is slightly delayed compared to the direct signal. There is a little latency within the amplifier itself, but most of the delay depends on how far away the microphone was from the speaker. If it was close-miked, e.g. within an inch of the cone, the phase difference won't be noticeable on a bass.  It's only if you set the mic back a foot or more from the speaker that phase will become an issue.
 
You've got a lot more room for sloppiness with bass than other instruments, due to the longer wavelengths, but sometimes even a 0.5 ms shift can make an audible difference even on bass. That's equivalent to having the microphone 6 inches from the speaker.
 
If you are combining two separate bass tracks, e.g. two synths/samplers or a synth + real bass guitar, then you'll definitely want to fiddle with the phase (probably not the polarity button though). When I'm experimenting with layering sounds I find it convenient to insert a delay plugin with millisecond resolution (the Sonitus Delay will do this) so I can sweep the delay while listening for the best combination.