Indeed, but that's part of the fun. I set up an ambush using a few constructs with fighter levels, taking combat expertise and combat reflexes. They intercepted the primary spell casters from the monk and warlock. I figured the primary spell casters would take a total defense action while the monk and warlock took a hit or two and reunited with their buff support. Instead, the group surprised me. The monk and warlock left the spell casters high and dry, separating to tackle both flanks surrounding them. The spell casters started taking 5 ft steps to attack with crossbows the flank on their end. They couldn't handle combat very long and had to use expeditious retreat to flee. The unbuffed monk eventually took a critical hit and dropped to -3. The Warlock had to move out of combat and activate her wand of cure moderate wounds on the monk, inuring a bunch of AoO. The monk used an emergency potion of mage armor on the first opportunity and the warlock began taking a total denfence stance until the monk destroyed the construct which crit him. I cheated a few rolls out of mercy and the party just barely survived the encounter.
However, a good group knows their limits and a good DM always provides reliable information to skillers who make appropriate knowledge and gather information checks. If a cautious DM provides a dangerous encounter, a knowledgable group should be able to take correct measures to handle an encounter safely. Such occurances should be uncommon, but provide good stories.