Technically, this isn't really a bug, more of a "gotcha" for those who first encounter it.
When compiling a GCC program that includes a .S assembly, a very bizarre error is thrown if you use a branch instruction that is out of reach...
5301:(.text+0x2326): relocation truncated to fit: R_AVR_7_PCREL against `no symbol'
I figured this out easily enough since I had only added a BRNE to my code, but this error could certainly be more descriptive and offer something like...
ERROR: Relative Branch Too Far (Line 5432 : BRNE)
This is similar to the no highlight on BRGE "bug" I found.. not really a bug, but could be fixed.