Space is added in the middle of subject when "Add Subject Prefix" is being used

[ezeitoun 1]

Hi, 
We are using Add Subject Prefix for every incoming e-mail (Adding "[EXTERNAL]" prefix,
We have noticed that on e-mails with "long" subject, Not clear why on some e-mails it happens, some it doesnt:

example (Also as seen on the client):
With the Problem: [EXTERNAL] Bea Alonso Takes the Lead of Dale t’s Global Product Marketing Group
Without the Problem: [EXTERNAL] BT Sport and Samsung kick-off 8K sports broadcasting in the UK

Any Ideas?