I very often find chord tabs with "mixed" key signatures.

For example, whichever tabbing program, might put the chords as, "Bb, G#, & D#.

OK, the Bb is correct, but the other 2 should be Ab & Eb, respectively.
As Eb would be the "I" or tonic chord, and Ab & Bb, the "IV & V" chords respectively.

In practice, the key of D# would always be reached en-harmonically via Eb. (Unless of course the sheet music was specifically for transposition purposes).

What gives?

(I apologize if this has been asked and answered too many times in the past).

This tab of, "Danny Boy", is a prime example of what I'm talking about: https://tabs.ultimate-guitar.com/g/glen_campbell/danny_boy_crd.htm
Typically, it would be because the tabber isn't well-versed in theory and isn't fully aware of enharmonics and properly notating the correct chords.
Skip the username, call me Billy
I concur with aerosmithfan95 as that being the most common reason.

However, in my own chording charts for guitar I will often us A#, D# etc, since on the fly I find them faster to read and find without missing a beat on guitar. To me they are more intuitive on a guitar than Bb and Eb, etc. Yet, if I was writing my charts to predominantly play on the piano then A# and D# would make me do a double-take and I might miss the beat as on that instrument I've always known them as Bb and Eb. Just a personal oddity I guess that defies music theory...
Anyone know if mixing sharps and flats really messes with the transpose function? I've been told it does but I've never seen it myself.
It does, as does mixing "H" and "B".
Glad to cross paths with you on this adventure called life
Quote by Jet Penguin
lots of flirting with the other key without confirming. JUST LIKE THEIR LOVE IN THE MOVIE OH DAMN.
Quote by Hail
you're acting like you have perfect pitch or something