A few bugs I've picked up on while watching a certain other person.

• Quark Towers - These... are glitchy now. They use a 2 second slow beam to hit a bunch of guys at 64 damage, pause a second, and then fires the beam again from the same point. This makes it worse than the 1 second fast beam because it's missing more targets like this. Also, the tooltip is misleading and should at least say 3 seconds if it's going to do that weird attack.
• Velocity Towers - Celerity is fine. The level 2, Velocity, does the new damage... at the old speed. It's horrible right now.
• Flamethrower + Money - This still isn't working. It's really problematic because that's a great 4-elemental combo build, where flamethrower really relies on single target damage, and unless you grab laser instead, the money tower's ability to get extra gold doesn't work, therefore making it a not-so-great tower.

Some other random bugs I've gotten over the last few months, one of them might be player specific (I always go orange, player 6).

• Mildew Towers - There is a specific spot (orange, player 6, have not tested it on any other spot) where the mildew tower's shot will fire to the point where it's supposed to return, and instead of returning, it goes on. Far left of the middle island, bottom side of it. Place a Mildew Tower there, and when creeps come down for the second pass on the bottom side, it will shoot them (when firing approximately straight down) and get this bug. Sorry, I don't have the access to post a screenshot or replay of this right now, I'll try to get one up later.
• Jet Towers - Using a specific timing (I have not entirely figured out what it is), there is a way to attack ground is two spots at the same time. Something to do with hitting "stop" and "attack ground" again within a short period of time probably. It's weird, and if it's pulled off, it's temporarily overpowered (until you need to upgrade it to the next one). I outlined the bug here, w/ a screenshot.

Once I get access to a computer that can play EleTD, I'll be able to test more things out.

The Quark Tower is not a bug. Missing the creeps was the point. It does more than 3x the damage of the 1 second beam.

Fixed Velocity. Flamethrower will take longer. Other two, I dunno.