Low Nimble Feet Won't End

Description of the bug: When using Nimble Feet in conjunction with Dark Sight below level 20, Nimble Feet does not end until Dark Sight ends. It's a very minor bug that honestly just makes it easier to get across the maps quickly without being hit, though arguably that wuld usually be saved for later levels. At level 20, Dark Sight no longer affects speed related skills.

What is supposed to happen?: Nimble Feet is supposed to be overwritten when using Dark Sight below level 20. It's also supposed to end, but it doesn't (unless Dark Sight goes off).

Where did you find and/or notice this bug?: Was leveling my new theif.

A step-by-step guide to re-producing this bug (optional): Step 1, make a thief. Step 2 use Nimble Feet. Step 3 use Dark Sight below level 20. Step 4 zoom zoom!

Extra info: just clarifying, by level 20 I mean the skill level, not the character level.