Save using Masterwork v.2h. Repeatable crash occurs shortly or can be caused linked to job cancellation of the masterwork modded reaction [REACTION:BLOCK_BOULDER]. If the save is left to run the crash should occur shortly. The jobs are currently running on three Stonecutter's workshops on Z-level -9, slightly to the left of the Slag pits. If the jobs in either of the active workshops (the top two) are cancelled the crash occurs immeadiately. If the inactive job is cancelled it does not cause the crash. The workshops are managed via a vanilla DF give command from the Bar/Block stockpile immediately above them and via a DF hack workflow command regulating "workflow amount BLOCKS//CONCRETE 200". Removing either or both of those prior to unpausing did not impact the crash.

If I suspend the job rendering it inactive and then cancel it everything appears to proceed fine, so the crash appears to only occur when an active BLOCK_BOULDER reaction is cancelled. If I proceed shortly and then recreate the reactions the crash occurs again.

This is a slightly modified version of the current masterwork raws, I changed the STEAM_ENGINE from a furnace to a workshop and slightly tweaked some pet names (to differentiate genders), and a few additional reactions (generally more specific examples (for instance the added MAKE_FUNGIPAPER reaction). But haven't made any changes to the reaction that is causing the crash.

System details
Mac OS 10.8.3
MacBook Pro 2.4 GHz Intel Core i5