Problem with CDU VNAV and Step Logic

[psolk 3,040]

Ok, So I have another one for you.I am currently doing LLBG-KEWR. Took off with 240000 lbs of fuel and initial CRZ Alt of 320 to burn off some fuel. ~ 2 1/2 hours into flight OPT alt went to 33100 and the CDU said Step NOW to 340. I commanded 340 on the MCP, entered it and VNAV disconnected. Knowing the plane was telling me she was not ready yet I dial 320 back in, re-entered and VNAV re-engaged. Well I am now 3 hours 40 minutes into the flight. OPT ALT says 34100, Step still shows NOW but if I enter 340 and execute it VNAV disconnects.Spd is .850So I decided to maually dial in .850 and a 500 FPM climb from 320 to 340 which is no problem. Got up to 340 and VNAV now engages again. Now yes, I know all about how a r/w pilot would rarely use VNAV for a mid flight step anyway but I just find it weird how the CDU just seems to lose its bearings opposed to giving an UNABLE CRZ ALT or something...It took me a while to learn how to get VNAV to re-engage after it shuts itself down like that and you lose your SEL SPD on the Prog page...It seems to me like there is still an issue with the STEP logic of the CDU. Something isn't happy even when she tells you step NOW.Still flying though, got VNAV engaged now at 340 and all is well with about 8 hours left, almost 4 gone. Stayed home from work in the States to watch the Arsenal V Barcelona match live... Wierd how you all play football with your feet... Where is the logic in that LOL-PaulPrimary RigLiquid CooledAMD FX-57 @ 3 gigsAsus A8NSLI-Premium2 gigs Corsair XMS PC3500LL 2 3 2 6 1TXFX 7900 GTX 690/1750XFX 7800 GTX 515/135024 inch Widescreen LCDDual 19 inch LCD'sRaid-0+1PCPower and Cooling 1khttp://home.comcast.net/~psolk/3monitorsa.htmlBackup RigAMD 4000 San Diego @ 2.72 Gigs Kingston Corsair XMS CL2XFX 7800 GTX 515/1350 Raid-0

[Guest D17S]

Doesn't seem like a step problem . . . more like a Vnav CRZ altitude reset problem. In cruise, pull up the Vnav CRZ page. (Pls note: Make sure you are further than 50 miles from TOD. If you dial in a lower altitude then, you shift to the Descent mode and initiate a