This is a list of known bugs and workarounds, if known.

Bug Comment
In the campaign, the enemy doesn't attack An especially nasty bug that really kills the fun. It can be helped by restarting the game and subsequently the respective mission.
Fallen units lose particle effects This happens with Keran Kessertin, Vangarath, Summoners, Void Walkers, Control Forms and the like, especially after a game was interrupted and the game program was closed in the meantime. No known solution (it is only a cosmetic effect, though, that doesn't interfere with the game mechanics)
Defensive buildings cannot be built Can happen to any faction. E.g. you want to place a Scout Tower closely to another one and the Peasant stands in front of the semitransparent building and does nothing. No known solution, but it is possible to place the next tower so far away from the other that this bug doesn't occur anymore (with any given strategic implications)
Warlock doesn't attack The Warlock theoretically has an attack of 50 (type Summoned). It is, however, not possible to attack anything. There is always the prompt "Invalid Target".
Units "hang" on the map This is a rare bug that happens on some maps. When it happens, the units hang on a specific point of the map although they would have a movement order. To solve the problem, give the unit new orders to move in the opposite direction for a short time and then give the old order.
Woodcutters on strike This bug can occur with any faction and makes worker units tasked to collect wood "forget" their task and stand idly in front of a tree. It apparently is a pathfinder bug. When ordering the unit to move away a bit and then re-issue the wood cutting order, everything should continue normally.