When trying this on a trombone, I hear the grace note as a separate (short) note, but not the following rest. This is even true when I turn off playback for the grace note (in the Speedy Entry Edit Frame) and even when I turn off playback for the rest. So I assume the result is produced by the glissando itself, which may be appropriate.

I don't think so. When I have a regular note, followed by a grace note, followed by a rest, and place a glissando or tab slide between the regular and grace notes, I hear the glissando from the first (normal) note to the second, followed by a very brief sustain on the second (grace) note, followed by a note of random pitch for the duration of the rest immediately following the second note. If I insert a "grace rest" (which can then optionally be hidden using Speedy Edit's "o" option) between the grace note and the rest, I hear the glissando with the slight sustain on the terminal pitch, followed by silence for the duration of the normal rest, which is what should be playing. (Have you tried it on guitar or bass, using Finale v26?)

This is not "normal" behavior, as earlier versions of Finale (i.e., Finale 2012) didn't have this "stray" unintended note-in-place-of-rest anomaly. It must be a bug in the playback system. I don't know if it's specific to version 26, or if it manifested earlier, but Finale should fix it in their next update for version 26!

Clearly the problem you experience should not happen, but in my instance of the program (starting with a new file) I cannot replicate your experience of a random note following the gliss.

The problem is not specific to glissandos--it is specific to any case in which a grace note precedes a (non-grace) rest. And I have had the problem when starting with a new file. If I enter a grace note followed by a normal rest, I get a rapid note of the indicated pitch (normal) followed by a random note for the duration of the rest (not normal). If I place a "grace rest" between the grace note and the normal rest, I get a rapid note followed by silence, which is what I would expect. I have not had this problem with Finale 2012, but I have had it with Finale v26--both with my old laptop and my current one. If you have Finale v26, try entering any music sequence in which a grace note immediately precedes a normal rest, and see what happens. Use "normal" (default) Human Playback settings (don't have any playback for grace notes or rests disabled) and Speedy Edit.

PS. I should have clarified earlier that the problem concerns grace notes preceding rest in general. I only brought up glissandos to explain why I was using this otherwise unorthodox musical syntax, and may in doing so confused people about the true nature of the problem.

What instrument are you using? I still cannot replicate your results on my machine.

Have you used the "Submit a request" link at the top of this page to submit a sample document directly to Finale Support for their analysis?

Staves configured by Score Manager for guitar and bass guitar. Notes entered manually in staves using Speedy Edit.