Seeing a loophole to be exploited between the loose language of the law and the clear intent, when it came time to shut down the government, furlough workers, and stop
checks from being issued, they got a convenient legal ruling that said, yes, suspending their own pay is considered altering the pay of Congress (because the law didn't just say pay raises)
during the same session, therefore, it is illegal for them not to collect their paychecks
during a
shutdown.