Tosafos says that according to some the heter of ta'am l'fgam (bad flavor) only applies to items that would be nullified in 60x heter to issur, but wouldn't apply to foods that are assur b'mashehu and are never batul. The rationale is a simple one - to permit ta'am l'gam we require 2 concepts: 1. only good flavor spreads issur until 60x, not bad flavors. 2. the minute amount of issur that we consider there to be in the flavor is batul b'rov in the majority of heter. Since we can only permit ta'am l'fgam based on both these assumptions, when the issur is not batul and the second reason isn't applicable we can't be matir foods even if it gives a bad flavor.
Tosafos rejects this logic by differentiating between an issur ma'shehu that falls into the same min, and ta'am l'fgam even when the item of heter and issur is exactly the same. R. Akiva Eiger (gilyon ha'shas) explains the rationale that since Tosafos is working in Abaye that we categorize issurim based on taste rather than name, any issur that gives a bad flavor doesn't have the same taste as the heter and is considered a min b'sheino mino (different item). Therefore, even if the item of issur is identical with that of heter (min b'mino), since the issur gives a bad flavor in the heter, it is always categorized as min b'sheino mino. No bitul is necessary to permit it because the only issur that exists is issur of flavor which is completely lost in the heter and would be permitted even by an issur that has no bitul. However, Tosafos seems to apply this concept even according to the halacha where we pasken like Rava and categorize issurim based on name. R. Akiva Eiger asks, it should follow that when we categorize based on name, even if an issur is ta'am l'fgam that falls into heter of the identical min, it should qualify as min b'mino (since the only distinction is flavor and we don't categorize based on flavor). By min b'mino we forbid the item b'mashehu, therefore we shouldn't be able to permit an item of issur that is nosein ta'am l'fgam that get mixed with an identical item (min b'mino).