There are a few instructions that are functionally equivalent. It is possible that one of the assemblers has the ability to auto convert equivalent behaviour instructions into smaller instructions that do the exactly the same thing. That is fairly common in assemblers. If one of the assemblers had a normalisation phase where they treat multiple forms of the same instruction as the same thing prior to checking if a more compact encoding is possible then that normalisation phase could be generating a same size instruction with same behaviour but with a different encoding. A small number of bytes different with same behaviour is what I would expect from a reassembly like this.

The proof of the pudding would be to have a look at what the differing bytes were encoding.