Izdahl becomes seriously concerned about some of the changes to Armando, in The Architect’s Guardian, Chapter 25. Here’s a portion:
Armando was indeed in the backyard but Izdahl was surprised and concerned by what he saw. His lover was kneeling, swaying backwards and forwards with his eyes closed. He was also speaking in a language which he was unlikely to have ever learned. While Izdahl could understand some of the words, much of it was difficult for him to grasp. He was able to recognize a few words and realized that Armando was chanting in one of the three main ancient Nitelge dialects. Izdahl was unsure how Armando could even know the phrases he kept on repeating.