The screenshot shows you are tuned to the FS ATC frequency and they are not necessarily the same. Let me explain...
PFE uses the FS frequencies extracted from FS by MakeRwys, but Center frequencies are not provided. Why? I don't know, that's a question for Pete Dowson (author of MakeRwys). It's probably because it is too complex to provide meaningful data. Washington Center for instance has more than one frequency, dependant on what sector you're in. PFE's database for control centres currently shows there are 46 sectors within the Washington area, each with their own frequency, which is not necessarily unique. To get PFE to work exactly the same as FS would be a daunting task and in my opinion pointless. It only becomes apparent there are slight differences if, like yourself, you are trying to run both FS and PFE ATC together for comparison purposes.
Does it really matter if they don't match exactly every time? You surely can't be concerned about real world accuracy because the FS database must be at least 8 years old now, so it's well out of date.
Here's a list of PFE's Washington Control Centre frequencies... there are 90 control center areas in PFE's world, made up of over 2,000 sectors.
124.05
118.00
127.90
132.55
134.53
134.53
121.67
133.12
121.25
128.52
132.50
134.62
127.70
127.42
132.22
133.25
118.92
124.25
133.82
132.25
133.72
135.40
127.92
135.30
135.20
133.85
135.50
123.85
132.55
124.50
118.75
127.75
125.45
132.52
134.50
134.25
133.65
132.77
133.90
118.82
134.15
120.65
133.97
133.27
133.20
128.60