Piano roll edits ignored until second playthrough [2016.08]

Having MIDI FX plugins in the project will cause that, even if they're not on the track you're editing. This goes way back.

I reported a related issue with MIDI buffering when looping with MFX that was a bigger problem for me, and that got fixed some time ago. I don't do much editing during playback, so I never reported this particular manifestation. I suspect it may be an inevitable side-effect of the extra buffering time needed to process MFX. 

Yeah, I'm guessing that yet again I'm running into issues because I do all my Piano Roll editing on-the-fly (during playback).  The Cakewalk developers and/or QA team don't seem to be doing very much on-the-fly editing during their testing, which is unfortunate for me (but perhaps not for the other 99% of Sonar users).
 
Well, at least there is an easy workaround: never use MIDI FX.  I've gone 15 years without using them until this project, so I can definitely afford to ignore them for another decade or so more!  (Although gone are any of my plans to develop my own MIDI FX, which is something that was in the back of my mind...)
 
Thanks for clarifying the issue!

Tripecac
Yeah, I'm guessing that yet again I'm running into issues because I do all my Piano Roll editing on-the-fly (during playback).  The Cakewalk developers and/or QA team don't seem to be doing very much on-the-fly editing during their testing, which is unfortunate for me (but perhaps not for the other 99% of Sonar users).

There was a time when you couldn't do any editing in MIDI sequencers during playback; you had to stop, edit, then restart. It was a huge deal when Steinberg announced a version of Cubase where you could do some editing while the engine was still running.
 
This has improved over the years but there are still operations that will either stop the engine temporarily, or require a stop/restart. Whether it's possible to change the MIDI FX architecture in SONAR to get around this issue, I don't know. FWIW you don't have to stop and restart if the section is looped; the data will refresh on the next pass.

Even normal MIDI buffering will cause a little of this, but it's usually not noticeable unless you're trying to make changes just a beat or two ahead of the Now time, which is difficult to do with any accuracy.
 
If you're looping several bars, it shouldn't be a big deal, and you can always use the various timeline navigation methods to jump the Now time back without stopping the transport - Prev/Next Measure are my goto shortcuts (non-default keybindings) for this.