Outcast is correct that the bug is cosmetic, but it can make it impossible to aim the weapon properly, so here's the fix:
So long as the accuracy of the beam is set to a number greater than zero, it'll display correctly. I actually discovered this by accident months ago and made a patch which lives permanently in my plugins folder, but never got around to posting it. In the meantime, anyone who wants it can get hold of a copy by e-mailing me at rcourt01@bcuc.ac.uk
To make your own patch, make a copy of the EV/O Sample Plug-in and rename it. Open it using ResEdit, and copy in the "weap" resource for the Zidegar Phased Beam from Override Data 2 in the main folder. Find the field called "innaccuracy" (or similar, I can't quite remember off the top of my head) and enter a positive, non-zero value. Keep it small, because this is the number of degrees of variation the weapon will display to either side of the centreline. Save the plug, close ResEdit and you're done.
Cheers,
Rooster, also returning after a long hiatus.