If you check the help system on this function, you'll find that the codes for each modifier keys add up to unique totals so if you want to script a halt to your script that detects multiple modifier keys held down, you check for the sum of them. This could detect the ctrl-shift-option or ctrl-shift-Alt as the halt combination for your script.
For More Information on this bug, see: SHIFT to open file with password promtp, when importing
This is one of many acknowledged bugs that can be found in the Known Bug List here in the Report an Issue section of the forum.
It can also be downloaded as a database file from: http://www.4shared.com/file/8orL8apk/FMP_Bugs.html