During a new adventure, I picked up Rasaad, the last new NPC I had yet to have come along. So bear in mind, this is also the first Monk experience I have.
When Rasaad gained enough experience for Level 2, he has 7 in Stealth.
I have 10 points to add to Move Silently, Find Traps and Hide in Shadows.
If I use any of those 10 points on Stealth with the + button, Stealth drops to 1 and that's it. I can continue to use the remaining points on Move Silently, Find Traps and Hide in Shadows.
I can also continue to use the + button on Stealth, until all points are used and Stealth vanishes completely. The Accept button becomes activated at this point.
If I use any of the 10 points on Move Silently, Find Traps or Hide in Shadows, Stealth vanishes as well and the Accept button activates.
Level Up with all available options. 10 points to distribute.
Level up with a point distributed to Stealth. Drops Stealth to 1; 8 points remaining to distribute.
Level up with all points distributed to Stealth. Stealth is removed from the screen; Accept button becomes available.
I am using a graphic mod (to change blue to brown) and Paint Portraits for NPCs.
Removing the graphic mod results in the same quirk.