Does my PSP hates my Mac?

So I have a new Mac and I plug in my home brewed psp into my mac and whenever I delete an .iso or any file off my PSP Memory stick, finder still says I have the same amount of space left or even less space available after deleting something. I have cfw 5.50 GEN-D (full). This only happens when i delete something from my psp. I also now cant switch my usb device to flash0 or flash1 or umd or any of them, just memory stick. Is it because my psp is in a windows format and i use a mac or is it due to the cfw version i have? thanks