Already got it. I have many lines like that in this file and can repro this effect on any of them.
Its related to having an error in the expression and then correcting it. Lets recap:
Original code was
if ( Sim.CreditTypeBehaviour.ToString().Equals(CreditTypeBehaviour.AutomobilePrivate.ToString())
|| Sim.CreditTypeBehaviour.ToString().Equals(CreditTypeBehaviour.AutomobileEnterprise.ToString())
|| Sim.CreditTypeBehaviour.ToString().Equals(CreditTypeBehaviour.EquipmentEnterprise.ToString())
|| Sim.CreditTypeBehaviour.ToString().Equals(CreditTypeBehaviour.MortgageLoanEnterprise.ToString()))
(Please ignore the various levels of stupidity in this code, written by an JS coder years ago) Then I edited it to
if ( Sim.CreditTypeBehaviour.Equals(CreditTypeBehaviour.AutomobilePrivate)
|| Sim.CreditTypeBehaviour.Equals(CreditTypeBehaviour.AutomobileEnterprise)
|| Sim.CreditTypeBehaviour.Equals(CreditTypeBehaviour.EquipmentEnterprise)
|| Sim.CreditTypeBehaviour.Equals(CreditTypeBehaviour.MortgageLoanEnterprise)
Notice the missing last closing bracket? Yes, I deleted one too many, thus the line was marked with the squiggly red line, indicating error. Now the erroneous italic started, even after adding the missing bracket, it continues to show the alternating italics on Equals(). After scrolling around the lines get redrawn with correct italics.