Evergreen is generating BFG tickets for fail->fail transitions when only pass->fail transitions configured

I realized that consecutive commits had BFG tickets created for them while going through the BFG tickets linked to BF-9759. I wouldn't ordinarily expect stepback to lead to the generation of BFG tickets but maybe there's some weird interaction with EVG-3645 going on?

• BFG-81063
  • https://evergreen.mongodb.com/task/mongodb_mongo_master_ubuntu1604_arm64_mobile_jstestfuzz_211b5c3006f89e8235dd6d795d0c64defc77030d_18_06_08_22_18_23
• BFG-81067
  • https://evergreen.mongodb.com/task/mongodb_mongo_master_ubuntu1604_arm64_mobile_jstestfuzz_8fae595c44b14aa61951ba413e293449c2b49866_18_06_08_21_11_33
• BFG-81072
  • https://evergreen.mongodb.com/task/mongodb_mongo_master_ubuntu1604_arm64_mobile_jstestfuzz_72784578190b44abe381e3a181adc309a1bd4cb1_18_06_08_20_52_08
• BFG-81074
  • https://evergreen.mongodb.com/task/mongodb_mongo_master_ubuntu1604_arm64_mobile_jstestfuzz_c68e6339eac6228e97f7eb3af7bcac506ce3d9e3_18_06_08_20_49_16
• BFG-81078
  • https://evergreen.mongodb.com/task/mongodb_mongo_master_ubuntu1604_arm64_mobile_jstestfuzz_e88605e272251362d16c416791434d56acfadfa9_18_06_08_20_45_51