I've been a professional C, Perl, PHP and Python developer.
I'm an ex-sysadmin from the late 20th century.
These days I do more Javascript and CSS and whatnot, and promote UX and accessibility.
Definitely, the expectations need to be set up-front and pay negotiated to reflect the extra work, either as an overall salary increase or as overtime pay for non-exempt workers.
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We're a place where coders share, stay up-to-date and grow their careers.
I used to do this as a sysadmin, and these days I sometimes do it as a developer.
It's ok.
Don't let them make you do it on the regular without getting paid for it!
Definitely, the expectations need to be set up-front and pay negotiated to reflect the extra work, either as an overall salary increase or as overtime pay for non-exempt workers.