Very sorry, Matthew - got sidetracked. Am going through testing that now and will get back to you. (I temporarily resolved the immediate problem -- had to pull down a 'sale' banner that had ended -- so simply opted to overwrite the image file outside of the plugin)
I'm not using any caching at the wordpress level -- had to disable Total Cache long ago as it caused untold issues; and I had no difficulty editing slide images 3 weeks ago (with no other plugin changes, other than updates, since that time)
I am also not able to save edited text/ALT text on a slide.
I DO get an alert from my Firewall plugin each time I attempt to edit a slide -- "This may be a "WordPress-Specific SQL Injection Attack."