Insertion of extra OFS character into output string

[H]

I am a newcomer to awk and have run into an issue I have not figured out yet... 
My platform is CentOS 7 running awk 4.0.2, the default version.

The following awk statement generates an extra tab character between fields 1 
and 2, regardless of the data in the file:

awk 'BEGIN{FS=","; FPAT="([^,]*)|(\"[^\"]+\")"; OFS="\t"} {$1=$1; gsub(/"/, 
""); print}' somefile.csv

If i change the statement to:

awk 'BEGIN{FS=","; FPAT="([^,]*)|(\"[^\"]+\")"; OFS="\t"} {$2=$2; gsub(/"/, 
""); print}' somefile.csv

an extra OFS character is inserted between fields two and three. I can add that 
removing the gsub() in either of the two examples does not affect the results.

Might this be a bug in 4.0.2 or a feature I have not yet understood?