Possibly Weird Behavior Regarding First Lines Which are Invisible?

[Jaft]

So I have a buffer; let's say 9 lines. And I have a function which runs 
(previous-line) (beginning-of-line 1) and said function is bound to a key 
(let's say <up>).
So I apply a text-property of 'invisible using (pos-bol) of the first line and 
(1+ (pos-eol)) in order to get the first line to disappear, like it's not even 
there.
If I'm on line 3 and M-: my function, it does what I'd expect and (point) will 
return the (pos-bol) of the second line. But, if I execute my function by 
pressing <up> from line 3, (point) keeps returning back 1, the point of the 
beginning of line 1 rather than the point at the beginning of line 2.
Is this expected behavior? I'd be less weirded out if running code through M-: 
gave back similar results but I get what I'd expect to happen no matter what 
code I run and only the unexpected behavior when running the exact same code 
via a key binding.
I'm running version 29.1 (GTK+ version 3.24.37 but through the terminal; I 
wouldn't expect these to affect anything as much as the Emacs version, though. 
On Guix).