Difference between PORT and LATCH on PIC 18F

Question

I already read the datasheet and google but I still don\'t understand something.

In my case, I set PIN RC6 of a PIC18F26K20 in INPUT mode:

TRI

Answer 1

I recently experienced that writing on PORTx Ri (e.g. PORTC RC1) of PIC18F14K50 is ineffective when another PORTx Rj (e.g. PORTC RC0) was already set. I observed a peek in the oscilloscope on PORTx Ri but I was unable to sustain the output. This issue has vanished as soon as I was writing on LATx.

LATx writing looks mandatory on PIC18 and PORTx writing prohibited.