Super Mario Bros. Deluxe
Bugs/glitches

Yoshi is hungry...
In Challenge mode, if you get the final Yoshi Egg along with the last Red Coins and/or Score award, your photo album will not get the picture for the Yoshi Eggs or the award you got with them. To prevent the glitch from not showing the pictures in the album, play in any game mode and save the game before entering the album.

If this happens to you, call Nintendo at 1-800-255-3700 and see if they can fix your game. Not sure if they still do this, but they would take your SMBDX cartridge, update your photo album, and send it back, free of charge. If all else fails, you can use the data erase code to start the whole game over.
--[Info: Dave Adams]

Small and Fiery Mario (Japanese version only)  [Screen shot]
As Fiery Mario, hit an enemy. While Mario is powering down, press Start to pause the game, and then choose "save." When you end the game and restart that saved game, Mario will either be (depending on your timing) small, Fiery, or small and Fiery! Unlike the small & Fiery bug in the original SMB, Mario is really small, and the fireballs will shoot out of nowhere from above his head. Since the game considers Mario to be "small," one hit will kill him. Touching a Super Mushroom will make Mario grow, and he'll still be wearing the Fiery outfit, and he'll still be able to shoot fire.
This bug was made possible by a change in the Japanese version of SMBDX, where Mario retains his form when you save your game.
--[Found by Deezer]

Bugs remaining from the original Super Mario Bros. are noted on the SMB bugs/glitches page.