Small reproducing example:
static SOMETHING : usize = 4usize;
Here, the 4usize doesn't get parsed correctly, and geany (which uses scintilla to do all the parsing) only marks 4us as the number, apparently parsing ize as a different, stand-alone identifier.
Here's a patch to fix this. See https://doc.rust-lang.org/stable/reference/tokens.html#suffixes for the allowed suffixes. Note that this patch removes the ability to parse the old 'is' and 'us' suffixes, but those are from pre 1.0 Rust, so nobody should care for their disappearance.
Committed as [0577ec].
Related
Commit: [0577ec]