GREP error: warning: cannot select font 'i'

I am in the process of learning the usage of iscsiadm and somehow I noticed a strange behavior of grep. Attempting to run the following grep command man iscsiadm | grep "aia" results in troff::498: warning: cannot select font 'i'. I played around and found out that the error does not occur when I grep for ia or ai, therefore, it must be caused by the specific pattern aia. Can anyone offer an explanation for this behavior? **EDIT** @telcoM I ran both command and both files contain the same error; They are in fact equal and yes, I don't see the error message in the console any longer. Both files contain the same error message as before. @TheNotoriousGBR It seems like you are right. I ran the command zgrep '\\fi' $(man -w iscsiadm) and in fact the capital "I" is missing:

\fiSNS\fR supported depends on build options, but is enabled by default.

Based on the previous result, it seems like the issue is not related to grep as many of you suggested but lies in fact inside the man page of iscsiadm itself. Should I let the title be as it is or change it to a more suitable one?