See image.   Same music, slow bounce vs fast bounce.   While they align and sound similar, clearly they are not the same. 
 
Edit -- all of my posts below relate to 'Bounce to Track' as used for a set of midi tracks sending data to a VST (Kontakt) and producing a new audio track.   As far as I know, 'bounce to track' as a means of manipulating audio files works ok.   
 
Made in Platinum, H version, all is midi sent to Kontakt5, and 'bounced' to generate audio.  Top one is fast bounce. 

afaia they're different processes - e.g., one of them ignores midi automation, though i forget which (fast?) but a baker or scook should probably confirm

just because the screen looks different,
does not mean they are different,
just because of what is involved to 'generate' the wav view.
 
if you pull them into the same file,
reverse phase,
they should null

clarification, it's real time bounce that ignores automation http://forum.cakewalk.com/Midi-Automation-not-Exported-with-Realtime-Export-m3084387.aspx i think? so if your "slow bounce" is "real time" then that would explain any differences

The MIDI-automation-not processed-with-fast-bounce-disabled issue was fixed some time ago - even before Platinum IIRC.
 
Although some synths may behave differently on fast bounce (and some need to have a "render" or "offline" mode explicitly enabled), another likely explanation is that some element in the synth/patch programming is deliberately "random" or not phase-locked so it never renders the same way twice, whether fast or slow. There are many synths and FX that won't null when bounced twice whether fast or not. The difference is audible when null-testing, but probably not in an A/B listening test.

all the freeze/bounce/export processing now uses the same process? good news! :-)
eta: of course, not including deliberately randomising functionality within particular plugs
thanks for clarifying :-)

It'd be an interesting test to clone the track and then bounce/freeze it twice in a row using the same settings and see if the waveforms still appear to be different. If they are, then that suggests there is some randomness in the patch, such as a chorus effect.
 
Most of the time with sample players you'll get identical results because you're just rendering the same samples. If you don't, then it's because of some effects being applied within the Kontakt instrument (which may not be visible).
 
The difference, as Steve points out, may not actually be audible. Contrary to intuition, two waveforms can be visually quite different and still sound the same. Sometimes, literally exactly the same.

batsbrew
if you pull them into the same file,
reverse phase,
they should null

Yes. That is the proper test. Even still they may not totally null because of things like "anti machine gun" features on drum programs, "round robin" sample playback, effects responding slightly differently through each pass, etc.
 
You would have to FREEZE everything (effects, synths and anything else that might produce any variations in the playback/mixdown) THEN do your comparison/null.
 
Edit: And I see others bringing up the same concepts.

Slow bounce does allow for automation.  You just have to be sure to check it in the options. 

Thanks for the ideas.   I've posted previously that no, reversing phase (at least as I know how) does not eliminate sound.  
 
I have trouble with the idea that slow bounce is WORSE than fast bounce, since effectively, slow bounce is what we work with just working on a mix and letting the midi drive the VST instrument.  
 
In my work, there is very little, pretty nearly NO, random change in how Kontakt responds to events.   
 
More comments welcome .. I clearly prefer a fast bounce, but if it isn't what I've slaved over for weeks to get to sound right, then I do not prefer fast!