The Hitech/Microchip 8-bit compilers have always been excellent, producing good, compact code. I've never encountered any bugs.
Doesn't sound like you used them much.
They were pretty solid and the best PIC C compiler until they bought out the new Pro version with OCG. That version was late and buggy as hell when it shipped in 2008 it slowly got less buggy over the last 5 years a period which included the Microchip acquisition of Hi-Tech.
For most of that 5 years I didn't consider it fit for use. I used the old version and wouldn't trust the Pro version without inspecting every instruction it generated - totally impractical for any large program.
There were various bugs with it not accepting valid C and cases where it just gives up trying to generate code for valid C.
Some of the others were truly horrendous.
I had one where it was using a timer register as a temporary during expression evaluation. Imagine debugging something where an expression intermediate value was being occasionally and randomly incremented. Another where a temporary file register should have been saved in interrupt context but wasn't so was occasionally and randomly corrupted - a bug which might not show up in days of testing.
In another evaluation of the second parameter of a function call overwrote the first parameter. These were bugs I noticed while trying to use it - I ended up using it very little. Today I still keep my fingers crossed.
Hi-Tech's policy of providing bug fixes without needing HPA kept me up to date for years without paying for HPA. Not having HPA meant I didn't get XC8 free, but a copy of C18 got me that anyway.
OCG is a good idea I think they underestimated how difficult it was and perhaps had financial and/or staff problems. The Microchip acquisition was strange with all of Hi-Tech's non-Microchip products just dumped and their 16 and 32 bit Microchip compilers promptly obsoleted. All Microchip got was the two 8 bit compilers. Microchip also adopted the pain in the arse licensing and activation scheme for all XC compilers.