Sorry to exhume - I used the search and found this thread - just thought I'd add my experience to it.
I replaced the brake compensator today and held it open with wire while I was bleeding the brakes. The nearside brake bled up quite quickly, but the offside took ages to bleed up. An interminably long time, in fact. I've not had this problem before, but I've not replaced a brake compensator valve before. It did bleed up in the end though - persevere and you'll get there.