How to reproduce:
1. Open attached project "Case_1008518-project".
2. Open Scene1.
3. Press on Cube and open Animator window.
4. Create parameter of type Bool named "Yes" and leave it at false.
5. Add "Yes" Condition to transition between Any State and New State 0 and set it to false.
6. Delete Bool parameter.
7. Create parameter of type Trigger named "Yes".
8. Run the scene.

Expected result: When replacing a parameter of type Bool/Int/Float with Trigger of the same name, Animator's transition changes it to Trigger, instead of leaving it as a previous one (Bool/Int/Float).
Actual result: When replacing a parameter of type Bool/Int/Float with Trigger of the same name, Animator's transition does not change parameter's type to Trigger but leaves it as a previous one (Bool/Int/Float). Therefore, even if Trigger is set, the transition does not happen, except if it is a false bool, then transition activates always.

Reproducible with - 2018.2.0a3, 2018.1.0b10, 2017.3.1p3, 2017.2.2f1, 2017.1.3p2, 5.6.5p2