The effects of a card, Orb of Firestorm, stay active even after the playing of the card is cancelled. This can be seen in "The Ancient Library" scenario of the "Fortress of the Stone Giants" adventure, where the villain, Mokmurian, has the following trait:
After playing the Firestorm Orb and cancelling it, the combat modifier becomes negative. Repeating the process makes it decrease further and further, while also increasing the number of dice involved in the combat check. This can be seen from around the 00:18 mark in this video:
https://www.youtube.com/watch?v=_katcBnhm7s
This was not the first time I encountered this bug - it happened to me on a previous attempt to clear the scenario - but this was the first time I was able to capture it on video.
For what it's worth, the video also contains evidence of another bug: if you pause it at the 00:07 mark, you'll see that Amiri is marked with an exclamation mark despite not being able to offer any assistance in the current check.
General (For all issues)
What platform are you on? Steam
What version of the OS are you running? Windows 10
What model is the device? Custom-built PC
What is your PFID#? PFID-70626BB4259D58FE
GameplayIs pass & play on? No
Is permadeath on? No
Tutorial, Story Mode, or Quest Mode? Story Mode
Characters in Party: Ezren, Amiri, Seoni, Merisiel
Location of each character: Ezren: Thassilonian Dungeon; Amiri: Giant Lair; Seoni: Thassilonian Library; Deeper Dungeons
Turn Order: Ezren, Amiri, Seoni, Merisiel
Scenario & Scenario Difficulty: Normal
What card was encountered when the issue occurred? Mokmurian, Firestorm Orb
Did the issue occur on the first explore or a subsequent explore? Don't recall
Did other characters aid the check? Yes, until I cancelled their aid
What did they use to aid it? Seoni used Blessing of Gorum
Was the encounter a Horde? No