Existing behavior: opcode 146 (cast spell at creature) is affected by wild surge when parameter2 is set to 0 (casting type = cast normally). However, opcode 148 (cast spell at point) is not affected by wild surge. As a result, you have inconsistent behavior where scrolls casting spells at a point always function in wild magic areas (such as AR3005) while other scrolls are affected normally.
Expected behavior: Either opcode 146 should not be affected by wild surge by default even when param2 is set to 0 OR opcode 148 should be affected by wild surge when param2 is set to 0. In the original post, I was originally more inclined to have opcode 146 not be affected by wild surge. After more thought I feel the reverse would make more sense - opcode 148 would be affected by wild surges only when param2 is set to 0 (cast spell normally). In this way, all types of scrolls would be affected by wild surge.
How to reproduce this: CLUA yourself to AR3005 (an wild magic area in Watcher's Keep), and CLUA yourself two scrolls SCRL6R (Spider Spawn) and SCRL6T (Protection From Normal Weapons). You should experiece this behavior when attempting to use the scrolls.