This is a regression because it's not possible in lgm16b4, but it's possible to set the min character greater than the max. That causes the for loop generating the preview to generate a bunch of out of range stuff. It seems 1.8.4 is the first version where this can be reproduced.
Closing as resolved by cef16322d84a05426fe8bde600adddcbc2551fe4 although additional validation of the ranges against the Unicode standard may still be a good idea.
This is a regression because it's not possible in lgm16b4, but it's possible to set the min character greater than the max. That causes the for loop generating the preview to generate a bunch of out of range stuff. It seems 1.8.4 is the first version where this can be reproduced.