Was doing a flight the other day a taking off during a snow storm and had selected 'REF A/I' to ON in the TRS page of the FMS before departure since I was getting an "Icing Condition" on the center display however some time after taking off and climbing and leaving the cloud layer containing the "ice," the white messages displaying that the system was still active did not go away. I confirmed that the anti-ice system was using bleed air via the status anti-ice page on the MFD. Even after reaching cruise of FL310 in clear, sunny conditions, the white system message remained.
So, a few minutes ago I decided to see if I could replicate the issue with NO 3rd party weather add-ons and encountered the same issue. Here are the steps I used to replicate. This on the latest version of Prepar3d (v4.5) and I was able to do it consistently with the 175:
1. Load up the simulator.
2. selected the "clear skies" weather scenario.
3. loaded the E-175 into the P3d default airport (KVPS)
4. on the FMS TRS page, selected REF A/I to ALL, ATTCS to ON, FLEX to ON and ECS to ON and used 15C as the remperature.
5. started, the engines, turned off the APU, set flaps for departure and climbed in clear conditions (15 degrees C on the ground to start) all the way to FL320 while having the anti-icing system active. The white text reads "A-I ENG 1-2 VLV OPEN," "A-I WING VLV OPEN," and "ENG TDS REF A-I ALL."
The only way to turn the system off was to depress the engine 1, wing, and engine 2 toggles from the overhead panel. That turned the system off but the white system message also stayed. Didn't matter if I switched to CLB-1, CLB-2 or CRZ (I usually leave it on AUTO).\
(These screenshots are from my test flight)