Why I have a negative income in Powerhouse Windows 3.1 game?

Game: Powerhouse

OS: Win 3.1 | dosbox

Problem: after upgrading the oil rig to 6 pressure pumps, it outputs 414 fuel to the adjacent refinery with 4 hydroskinning units. It outputs -315 of processed fuel to the adjacent generator with 2 steam converters, which output -258 electricity. This decreases my balance by -258 M$ each month.

Is this some sort of bug?

Saving and reloading the game and restarting the whole emulator doesn't help.

Update: Seems to be bug because when connecting pumps and refinery using pipes fixes this.

This might be a bug because:

1. When connecting pumps and refinery using the pipes this doesn't occur. (game may expect to use only the pipes / auto deliveries)
2. It looks like a variable overflow.
3. The game is extremely buggy and finding another bug is a common thing.