When defining app specific hotkeys to mouse buttons, such as "Spacebar" to mouse button 4. Holding keyboard modifier keys such as shift, BTT will revert back to global setting (Mine are set to dashboard), so pressing Button 4 with any modifier will call out dashboard. Unless I specifically define a modifier key combo, any unset keys will be forced to Global action. That makes it hard to use with other apps with multi modifier combination (like photoshop).
My current workaround is to set all possible modifier combinations (About 10 per key).
Affected input device:
Keyboard (Regular PC keyboard), Non Apple Mouse (Steelseries Sensei 310)
iMac Late 2013
MacOS High Sierra 10.13.6
BetterTouchTool version: 2.687