Do I have a MechJeb issue? MechJeb burning much more fuel than Rocket Equation calls for

[Poppa Wheelie]

I ran some tests a few days ago, looking to collect dV and fuel requirements for an upcoming Eve mission I'm planning.  With the ship below, I did the following:

• Cheat the vessel to Low Eve Orbit in Sandbox mode
• Run the sequence of steps shown in the spreadsheet, from bottom to top, starting with "Raise Ap to 64Mm" and ending with "Hohmann transfer to target".  I had MechJeb do all the burns.  In some cases I halted executing before it was finished, because I had reached the target and there was still dV remaining in the burn.

In every case:

• MechJeb burned more fuel than the Rocket Equation calls for.  Look at column E of the spreadsheet.  This is what the Rocket Equation calls for given the dry mass of column H and the dV of column D.  I spot checked some of these using this URL, which agreed with my numbers:  https://faxmachinen.com/ksp/fuel.html.  Now look at columns E and N.  E is the amount of fuel that should be required to burn the dV called for in column D, but column N is the fuel actually used.  They differ by quite a lot.
• MechJeb always started the burn "late", past the burn time divided by 2 time.  Even on the relatively short, low dV burns.

Do I have a MechJeb issue?  If so, do I need to report it on a different forum, with logs, etc.?  Or is this expected behavior?